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Slices of ice core, drilled from the depths of the Earth's ice sheets, reveal details of the planet's past climate.

Introduction

Ice cores are cylinders of ice drilled out of an ice sheet or glacier. Most ice core records come from Antarctica and Greenland, and the longest ice cores extend to 3km in depth. The oldest continuous ice core records to date extend 123,000 years in Greenland and 800,000 years in Antarctica. Ice cores contain information about past temperature, and about many other aspects of the environment. Crucially, the ice encloses small bubbles of air that contain a sample of the atmosphere - from these it is possible to measure directly the past concentration of gases (including carbon dioxide and methane) in the atmosphere.

Greenhouse gases and the recent past

Direct and continuous measurements of carbon dioxide (CO ₂) in the atmosphere extend back only to the 1950s. Ice core measurements allow us to extend this way back into the past. In an Antarctic core (Law Dome) with a very high snowfall rate, it has been possible to measure concentrations in air from as recently as the 1980s that is already enclosed in bubbles within the ice. Comparison with measurements made at South Pole station show that the ice core acts as a faithful recorder of atmospheric concentrations (see Fig. 1 overleaf), although we do have to be cautious, as artefacts can arise at sites with high concentrations of other impurities.

Antarctic ice cores show us that the concentration of CO ₂ was stable over the last millennium until the early 19th century. It then started to rise, and its concentration is now nearly 40% higher than it was before the industrial revolution (see Fig. 2 overleaf). Other measurements (e.g. isotopic data) confirm that the increase must be due to emissions of CO ₂ from fossil fuel usage and deforestation. Measurements from older ice cores (discussed below) confirm that both the magnitude and rate of the recent increase are almost certainly unprecedented over the last 800,000 years. The fastest large natural increase measured in older ice cores is around 20ppmv (parts per million by volume) in 1,000 years (a rate seen during Earth's emergence from the last ice age around 12,000 years ago). CO ₂ concentration increased by the same amount, 20ppmv, in the last 10 years! Methane (CH ₄), another important greenhouse gas, also shows a huge and unprecedented increase in concentration over the last two centuries. Its concentration is now much more than double its pre-industrial level. This is mainly due to the increase in emissions from sources such as rice fields, ruminant animals and landfills, that comes on top of natural emissions from wetlands and other sources.

Natural climate changes: glacial-interglacial cycles

By measuring the ratios of different water isotopes in polar ice cores, we can determine how temperature in Antarctica and Greenland has changed in the past. The oldest ice core we have was drilled by the European Project for Ice Coring in Antarctica (EPICA) from Dome C on the Antarctic plateau. It extends back 800,000 years and shows a succession of long, cold 'glacial' periods, interspersed roughly every 100,000 years by warm 'interglacial' periods (of which the last 11,000 years is the most recent). This succession of events is well-known from other records, and the coldest periods in Antarctica are the times when we had ice ages. Ice sheets extended over North America as far south as Wisconsin, and over Britain to south of The Wash.

The role of greenhouse gases in glacial-interglacial cycles

From the air in our oldest Antarctic ice core, we can see that CO ₂ changed in a remarkably similar way to Antarctic climate, with low concentrations during cold times, and high concentrations during warm periods (see Fig. 3 overleaf). This is entirely consistent with the idea that temperature and CO ₂ are intimately linked, and each acts to amplify changes in the other (what we call a positive feedback). It is believed that the warmings out of glacial periods are paced by changes in Earth's orbit around the Sun, but the tiny changes in climate this should cause are amplified, mainly by the resulting increase in CO ₂, and by the retreat of sea ice and ice sheets (which leads to less sunlight being reflected away). Looking at the warming out of the last glacial period in detail, we can see how remarkably closely Antarctic temperature and CO ₂ tracked each other. It is often said that the temperature 'leads' the CO ₂ during the warming out of a glacial period. On the most recent records, there is a hint that the temperature started to rise slightly (at most a few tenths of a degree) before the CO ₂, as expected if changes in Earth's orbit cause an initial small warming. But for most of the 6,000-year long 'transition', Antarctic temperature and CO ₂ rose together, consistent with the role of CO ₂ as an important amplifier of climate change (see Fig. 4 overleaf). In our modern era, of course, it is human emissions of CO ₂ that are expected to kick-start the sequence of events. We see no examples in the ice core record of a major increase in CO ₂ that was not accompanied by an increase in temperature. Methane concentration also tracks the glacial-interglacial changes, probably because there were less wetlands in the colder, drier glacial periods.

Abrupt climate changes

The climate changes described above were huge, but relatively gradual. However, ice cores have provided us with evidence that abrupt changes are also possible. During the last glacial period, Greenland experienced a sequence of very fast warmings (see Fig. 5 overleaf). The temperature increased by more than 10°C within 40 years. Other records show us that major changes in atmospheric circulation and climate were experienced all around the northern hemisphere. Antarctica and the Southern Ocean experienced a different pattern, consistent with the idea that these rapid jumps were caused by sudden changes in the transport of heat in the ocean. At this time, there was a huge ice sheet (the Laurentide) over northern North America. Freshwater delivered from the ice sheet to the North Atlantic was able periodically to disrupt the overturning of the ocean, causing the transport of tropical heat to the north to reduce and then suddenly increase again. While this mechanism cannot occur in the same way in today's world, it does show us that, at least regionally, the climate is capable of extraordinary changes within a human lifetime - rapid switches we certainly want to avoid experiencing.

Summary

Ice cores provide direct information about how greenhouse gas concentrations have changed in the past, and they also provide direct evidence that the climate can change abruptly under some circumstances. However, they provide no direct analogue for the future because the ice core era contains no periods with concentrations of CO2 comparable to those of the next century.

Factfile

Ice core. Cylinder of ice drilled out of an ice sheet or glacier. Most ice core records come from Antarctica and Greenland.

Ice cores contain information about past temperature, and about many other aspects of the environment.

Atmospheric carbon dioxide levels are now 40% higher than before the industrial revolution. This increase is due to fossil fuel usage and deforestation.

The magnitude and rate of the recent increase are almost certainly unprecedented over the last 800,000 years.

Methane also shows a huge and unprecedented increase in concentration over the last two centuries.

Data sources:

1. MacFarling Meure, C., and others: Law Dome CO2, CH4 and N2O ice core records extended to 2,000 years BP, Geophys. Res. Lett., 33, L14810, doi:10.1029/2006GL026152, 2006

2. Atmospheric data supplied by NOAA/ESRL

3. Friedli, H., and others: Ice core record of the 13C/12C ratio of atmospheric CO2 in the past two centuries, Nature, 324, 237-238, 1986

4. Siegenthaler, U., and others: Supporting evidence from the EPICA Dronning Maud Land ice core for atmospheric CO2 changes during the past millennium, Tellus Ser. B-Chem. Phys. Meteorol., 57, 51-57, 2005

5. Jouzel, J., and others: Orbital and millennial Antarctic climate variability over the last 800,000 years, Science, 317, 793-796, 2007

6. Lüthi, D., and others: High-resolution carbon dioxide concentration record 650,000-800,000 years before present, Nature, 453, 379-382, 2008

7. Monnin, E., and others: Atmospheric CO2 concentrations over the last glacial termination, Science, 291, 112-114, 2001 with data converted to the age scale of Parrenin, F., and others: The EDC3 chronology for the EPICA Dome C ice core, Climate of the Past, 3, 485-497, 2007

8. North Greenland Ice Core Project Members: High-resolution record of Northern Hemisphere climate extending into the last interglacial period, Nature, 431, 147-151, 2004

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Slices of ice core, drilled from the depths of the Earth's ice sheets, reveal details of the planet's past climate. Ice cores are cylinders of ice drilled out of an ice sheet or glacier. Most ice core records come from Antarctica and Greenland, and the longest ice cores extend to 3km in depth.

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OCR Geography A-level: Climate Change Revision - PMT

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Summary notes, articles and past exam questions for OCR Geography AS and A-Level Climate Change topic

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argument: burning biofuels and burying emissions can lower atmospheric co2

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argument: c02 would leak too slowly (thousands of years) to be a concern

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argument: ccs can be widely deployed on existing

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argument: ccs can dramatically slash emissions from fossil fuels

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argument: ccs can ensure that buried carbon will stay there

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argument: ccs delays inevitable transition to clean energy

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argument: ccs distracts attention and resources from clean energy

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argument: ccs doesn't have to be profitable to be a good idea

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argument: ccs is less cost-effective than renewable energy

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Debate: Carbon capture and storage - Debatepedia

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Carbon Capture and Storage (CCS) is a vital tool in the global fight against climate change. With its important application to the capture and storage of carbon dioxide emissions from power stations, CCS has a crucial role to play in tackling greenhouse gas emissions whilst maintaining security of supply. The International Energy Agency (IEA) has estimated that to halve global emissions by 2050 (widely believed to be required to limit the temperature rise to 2ºC), CCS will need to contribute one fifth of the required emissions reductions, both in the power sector as well as the industrial sector. In addition, the IEA have found that attempting to halve global emissions by 2050 without CCS, would increase costs by more than 70% per year.

To meet global 2050 goals, the IEA has projected that we will need 100 CCS projects around the world by 2020 and more than 3000 by 2050. This is a significant scale-up from current ambitions. There are very major benefits arising from the deployment of CCS in addition to climate mitigation.

When considering the capital investment in capture, transport and storage that will be needed to build these projected CCS projects, a picture emerges of a global market for CCS worth more than $5 trillion by 2050 (similar to the oil industry). In the UK alone, the government has estimated that CCS could be worth up to £6.5bn per year by 2030, creating up to 100,000 jobs.

Although it must be said that CCS projects are large, capital intensive projects, they provide extremely good value for money both in terms of cost per tonne of CO ₂ saved and per unit of clean electricity. For example, the costs of early demonstration projects has been estimated at €60-90 per tonne of CO ₂ with costs reducing to around €30-45 per tonne of CO ₂ by 2030.

There are also significant social benefits from the deployment of CCS. The supply chain for CCS will create a large variety of jobs for those communities living near a capture plant, pipeline or storage facility. Jobs will be required in core engineering and manufacturing sectors, as well as pipeline design, management and operation and a host of skills related to CO ₂ storage, including exploration and site characterisation, injection well construction and management. Many energy intensive manufacturing industries will in future be seen to be unsustainable without CCS. So the application of CCS will protect jobs and prosperity related to these industries. Developing networks of CCS pipeline networks will enable local prosperity through the longevity of regional industries.

The development and deployment of CCS will be very significant in ensuring that we are able to meet increasing energy demand and keep the lights on whilst minimising the environmental damage. The market for CCS is likely to be measured in the $trillions with the creation of a large variety of specialist jobs.
Judith Shapiro is a Policy Officer at the Carbon Capture and Storage Association

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Carbon Capture and Storage (CCS) is a vital tool in the global fight against climate change. With its important application to the capture and storage of carbon dioxide emissions from power stations, CCS has a crucial role to play in tackling greenhouse gas emissions whilst maintaining security of supply.

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Advantages and disadvantages of major CO2 capture technologies

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It is not possible to develop sub-scale oxy-combustion technology at existing power plants. An oxy-combustion power plant is an integrated plant and oxy-combustion technology development will require commitment of the whole power plant to the technology.

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National Institute of Environmental Health Sciences

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Climate and Human Health

Changes in the greenhouse gas concentrations and other drivers alter the global climate and bring about myriad human health consequences. Environmental consequences of climate change, such as extreme heat waves, rising sea-levels, changes in precipitation resulting in flooding and droughts, intense hurricanes, and degraded air quality, affect directly and indirectly the physical, social, and psychological health of humans. For instance, changes in precipitation are creating changes in the availability and quantity of water, as well as resulting in extreme weather events such as intense hurricanes and flooding. Climate change can be a driver of disease migration, as well as exacerbate health effects resulting from the release of toxic air pollutants in vulnerable populations such as children, the elderly, and those with asthma or cardiovascular disease.

Certain adverse health effects can be minimized or avoided with sound mitigation and adaptation strategies. Strategies for mitigating and adapting to climate change can prevent illness and death in people now, while also protecting the environment and health of future generations. Mitigation refers to actions being taken to reduce greenhouse gas emissions and to enhance the sinks that trap or remove carbon from the atmosphere. Adaptation refers to actions being taken to lessen the impact on health and the environment due to changes that cannot be prevented through mitigation. Appropriate mitigation and adaptation strategies will positively affect both climate change and the environment, and thereby positively affect human health. Some adaptation activities will directly improve human health through changes in our public health and health care infrastructure.

It is critical that adaptation and mitigation decisions and policies be developed with a sound basis in the best current science on climate change and its effects. There are gaps in our understanding of the relationship between climate change, the environment, and human health. In its 2010 report, A Human Health Perspective on Climate Change (Full Report) (4MB) , the NIEHS-led Interagency Working Group on Climate Change and Health identified major research areas that need to be further explored and understood. These include the following:

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Health Impacts - Climate and Human Health

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Changes in the greenhouse gas concentrations and other drivers alter the global climate and bring about myriad human health consequences. Environmental consequences of climate change, such as extreme heat waves, rising sea-levels, changes in precipitation resulting in flooding and droughts, intense hurricanes, and degraded air quality, affect directly and indirectly the physical, social, and psychological health of humans.

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Average surface temperatures on earth have risen more than 2°F over the past 100 years. During this time period, atmospheric levels of greenhouse gases such as carbon dioxide (CO2) and methane (CH4) have notably increased. This site explores the debate on whether climate change is caused by humans (also known as anthropogenic climate change).

The pro side argues rising levels of atmospheric greenhouse gases are a direct result of human activities such as burning fossil fuels, and that these increases are causing significant and increasingly severe climate changes including global warming, loss of sea ice, sea level rise, stronger storms, and more droughts. They contend that immediate international action to reduce greenhouse gas emissions is necessary to prevent dire climate changes.

The con side argues human-generated greenhouse gas emissions are too small to substantially change the earth's climate and that the planet is capable of absorbing those increases. They contend that warming over the 20th century resulted primarily from natural processes such as fluctuations in the sun's heat and ocean currents. They say the theory of human-caused global climate change is based on questionable measurements, faulty climate models, and misleading science. Read more background...

Pro & Con Arguments

Pro 3

The rise in atmospheric CO2 over the last century was clearly caused by human activity, as it occurred at a rate much faster than natural climate changes could produce.

Over the past 650,000 years, atmospheric CO2 levels did not rise above 300 ppm until the mid-20th century. Atmospheric levels of CO2 have risen from about 317 ppm in 1958 to 415 ppm in 2019. According to the Scripps Institution of Oceanology, the "extreme speed at which carbon dioxide concentrations are increasing is unprecedented. An increase of 10 parts per million might have needed 1,000 years or more to come to pass during ancient climate change events." Some climate models predict that by the end of the 21st century an additional 5°F-10°F of warming will occur.
Read More

Pro 4

The specific type of CO2 that is increasing in earth's atmosphere can be directly connected to human activity.

The US Environmental Protection Agency says that "Human activities are responsible for almost all of the increase in greenhouse gases in the atmosphere over the last 150 years."
Read More

Pro 5

Average temperatures on earth have increased at a rate far faster than can be explained by natural climate changes.
Read More

Pro 6

Natural changes in the sun's activity cannot explain 20th century global warming.
Read More

Pro 7

Global warming caused by human-produced greenhouse gases is causing the Arctic ice cap to melt at an increasing rate.
Read More

Pro 8

Sea levels are rising at an unprecedented rate due to human activities.

A study found that "significant acceleration" of sea-level rise occurred from 1870 to 2004. Between 1961 and 2003, global sea levels rose 8 inches; a 2019 UN report said they could rise by 3 feet in the next 80 years, displacing hundreds of millions of people. A study published in the Proceedings of the National Academy of Sciences concluded that the rate of sea level rise over the past century is unprecedented over the last 6,000 years.
Read More

Pro 10

Ocean temperatures are rising at an unprecedented rate due to anthropogenic global warming.
Read More

Pro 12

Human-caused global warming is changing weather systems and making heat waves and droughts more intense and more frequent.
Read More

Pro 13

Dramatic changes in precipitation, such as heavier storms and less snow, are another sign that humans are causing global climate change.

As human-produced greenhouse gases heat the planet, increased humidity (water vapor in the atmosphere) results. Water vapor is itself a greenhouse gas. In a process known as a positive feedback loop, more warming causes more humidity which causes even more warming. Higher humidity levels also cause changes in precipitation. According to a report published in the Proceedings of the National Academy of Sciences, the recorded changes in precipitation over land and oceans "are unlikely to arise purely due to natural climate variability."
Read More

Pro 14

Permafrost is melting at unprecedented rates due to global warming, causing further climate changes.
Read More

Con 1

Many scientists disagree that human activity is primarily responsible for global climate change.

A Purdue University survey found that 47% of climatologists challenge the idea that humans are primarily responsible for climate change and instead believe that climate change is caused by an equal combination of humans and the environment (37%), mostly by the environment (5%), or that there's not enough information to say (5%).
Read More

Con 2

Earth's climate has always warmed and cooled, and the 20th century rise in global temperature is within the bounds of natural temperature fluctuations over the past 3,000 years.

A study published in Nature found that "high temperatures - similar to those observed in the twentieth century before 1990 - occurred around AD 1000 to 1100" in the Northern Hemisphere. A study published in Boreas found that summer temperatures during the Roman Empire and Medieval periods were "consistently higher" than temperatures during the 20th century.
Read More

Con 3

Rising levels of atmospheric CO2 do not necessarily cause global warming.

Earth's climate record shows that warming has preceded, not followed, a rise in CO2. According to a study published in Science, measurements of ice core samples showed that over the last four climactic cycles (past 240,000 years), periods of natural global warming preceded global increases in CO2. The Proceedings of the National Academy of Sciences published a study of the earth's climate 460-445 million years ago which found that an intense period of glaciation, not warming, occurred when CO2 levels were 5 times higher than they are today. According to ecologist and former Director of Greenpeace International Patrick Moore, PhD, "there is some correlation, but little evidence, to support a direct causal relationship between CO2 and global temperature through the millennia."
Read More

Con 4

Human-produced CO2 is re-absorbed by oceans, forests, and other "carbon sinks," negating any climate changes.

A paper published in Asia-Pacific Journal of Atmospheric Sciences found that some climate models overstated how much warming would occur from additional C02 emissions. About 50% of the CO2 released by the burning of fossil fuels and other human activities has already been re-absorbed by the earth's carbon sinks. From 2002-2011, 26% of human-caused CO2 emissions were absorbed specifically by the world's oceans. A study published in the Proceedings of the National Academy of Sciences found evidence that forests are increasing their growth rates in response to elevated levels of CO2, which will in turn, lower atmospheric CO2 levels.
Read More

Con 5

CO2 is so saturated in earth's atmosphere that more CO2, manmade or natural, will have little impact on the climate.

According to the Heartland Institute's 2013 Nongovernmental International Panel on Climate Change (NIPCC) report, "it is likely rising atmospheric CO2 concentrations will have little impact on future climate."
Read More

Con 6

Global warming and cooling are primarily caused by fluctuations in the sun's heat (solar forcing), not by human activity.

According to a study published in the Journal of Atmospheric and Solar-Terrestrial Physics, 50-70% of warming throughout the 20th century could be associated with an increased amount of solar activity. Between 1900 and 2000 solar irradiance increased 0.19%, and correlated with the rise in US surface temperatures over the 20th century.

A study published in Energy & Environment wrote, "variations in solar activity and not the burning of fossil fuels are the direct cause of the observed multiyear variations in climatic responses." In a study by Willie Soon, PhD, Physicist at the Harvard-Smithsonian Center for Astrophysics, a strong correlation between solar radiation and temperatures in the Arctic over the past 130 years was identified.
Read More

Con 7

The rate of global warming has slowed over the last decade even though atmospheric CO2 continues to increase.
Read More

Con 8

Sea levels have been steadily rising for thousands of years, and the increase has nothing to do with humans.

According to Professor of Earth and Atmospheric Sciences at the Georgia Institute of Technology, Judith Curry, PhD, "it is clear that natural variability has dominated sea level rise during the 20th century, with changes in ocean heat content and changes in precipitation patterns."
Read More

Con 9

The acidity levels of the oceans are within past natural levels and the current rise in acidity is a natural fluctuation.

The pH of average ocean surface water is 8.1 and has only decreased 0.1 since the beginning of the industrial revolution (neutral is pH 7, acid is below pH 7). Science published a study of ocean acidity levels over the past 15 million years, finding that the "samples record surface seawater pH values that are within the range observed in the oceans today."
Read More

Con 10

A lot of climate change fears are based on predictions and inadequate or flawed computer climate models.

Climate models have been unable to simulate major known features of past climate such as the ice ages or the very warm climates of the Miocene, Eocene, and Cretaceous periods. If models cannot replicate past climate changes they should not be trusted to predict future climate changes. A Asia-Pacific Journal of Atmospheric Science study using observational data rather than computer climate models concluded that "the models are exaggerating climate sensitivity" and overestimate how fast the earth will warm as CO2 levels increase.
Read More

Con 11

Glaciers have been growing and receding for thousands of years due to natural causes, not human activity.

A study of ice cores published in Nature Geoscience said the current melting of glaciers in Western Antarctica was due to "atmospheric circulation changes" that have "caused rapid warming over the West Antarctic Ice Sheet" and cannot be directly attributed to human caused climate change. According to one of the study authors, "[i]f we could look back at this region of Antarctica in the 1940s and 1830s, we would find that the regional climate would look a lot like it does today, and I think we also would find the glaciers retreating much as they are today." According to Christian Schlüchter, Professor of Geology at the University of Bern, the retreat of glaciers in the Alps began in the mid-19th century, before large amounts of human caused CO2 had entered the atmosphere.
Read More

Con 12

Deep ocean currents, not human activity, are a primary driver of natural climate warming and cooling cycles.

Over the 20th century there have been two Arctic warming periods with a cooling period (1940-1970) in between. According to a study in Geophysical Research Letters, natural shifts in the ocean currents are the major cause of these climate changes, not human-generated greenhouse gases. William Gray, PhD, Emeritus Professor of Atmospheric Science at Colorado State University, said most of the climate changes over the last century are natural and "due to multi-decadal and multi-century changes in deep global ocean currents."
Read More

Con 13

Increased hurricane activity and other extreme weather events are a result of natural weather patterns, not human-caused climate change.
Read More

Did You Know?

1. A 2019 report from the Yale Program on Climate Change Communication found that 73% of Americans think global warming is occurring, marking a ten percentage point increase over Mar. 2015.

2. According to many peer-reviewed studies, over 97% of climate scientists agree that human activity is extremely likely to be the cause of global climate change.

3. A peer-reviewed study found that "up to 70% of the observed post-1850 climate change and warming could be associated to multiple solar cycles."

4. The Unites States makes up about 4% of the world's population but was responsible for nearly one-third of historical global greenhouse gas emissions.

5. A peer-reviewed study of the earth's climate 460-445 million years ago found that an intense period of glaciation, not warming, occurred when CO2 levels were 5 times higher than they are today.

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Climate Change - Pros & Cons - ProCon.org

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Average surface temperatures on earth have risen more than 2°F over the past 100 years. During this time period, atmospheric levels of greenhouse gases such as carbon dioxide (CO2) and methane (CH4) have notably increased. This site explores the debate on whether climate change is caused by humans (also known as anthropogenic climate change).

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How do you solve a problem like climate change playlist TEDTALKS

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How do you solve a problem like climate change playlist TEDTALKS

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How do you solve a problem like the climate crisis?

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We all know about the climate crisis. We all want to stay informed - but the information can be overwhelming. Watch these talks to hear what's at stake and find out what's being done.

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Psychology behind why people don't believe climate change is real

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Psychology behind why people don't believe climate change is real

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Why People Don't Believe In Climate Science

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Al Gore: The case for optimism on climate change

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Why is Al Gore optimistic about climate change? In this spirited talk, Gore asks three powerful questions about the man-made forces threatening to destroy our planet -- and the solutions we're designing to combat them. (Featuring Q&A with TED curator Chris Anderson)

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Background - 4 July, 2012

Why are sea levels rising?

The main cause of sea level rise today is global warming caused by human activity. This warming drives sea level rise in two main ways:

by warming ocean water; as it warms, water expands, taking up more space

by melting land-based ice (glaciers and ice sheets), sending more water to our oceans.

Today, is by far the biggest driver of global sea level rise.

Sea level rise past, present and future

So far sea levels have risen by about 20cm (since 1880). As global warming continues, the rate is speeding up, with sea levels currently rising at about 3mm per year.

Looking ahead, future sea level rise could total one meter or even more by the end of this century if emissions are not held in check.

Why is sea level rise dangerous?

Sea level rise has already worsened flooding caused by tropical cyclones and everyday high tides. Yet today about half of the world's population - three billion people - live within 200km of a coastline.

These coastal populations are growing and urbanising faster. People and infrastructure are crowding into vulnerable coastal areas. Most mega-cities are in coastal zones. Rising sea levels could inundate low-lying coastal areas unless cities spend billions to keep ocean waters at bay.

Water contamination, erosion and storm damage

Rising seas can send ocean water further inland. When this salt water contaminates it, fresh groundwater becomes useless for drinking or farming.

As waves reach higher and further, they cause more erosion damage on coastal lands. This damage becomes even worse during storms, when seawater and waves push still further inland, damaging more wildlife habitat, soil, buildings, and roads and other infrastructure.

Small island nations on the front line

People of small island nations are among the first and worst affected by sea level rise and climate change. Some small islets among the Pacific islands of the Republic of Kiribati have already disappeared beneath the rising ocean. Today, flooding on Kiribati regularly kills crops, contaminates drinking water, and floods homes.

Between 1.2 and 2.2 million people could displaced from the Caribbean and Indian and Pacific ocean islands with future sea level rise of between 0.5 and 2m (under 4 ° Celsius of warming).

What can be done about sea future level rise?

We cannot avoid some amount of future sea level rise. This is because emissions already in the atmosphere will "lock in" some future warming and sea level rise.

But the choices we make today and tomorrow will have a big effect on how much and how fast sea level rises beyond 2050. With s trong cuts to emissions, future sea level rise could be kept to between 28 and 61cm.

What is Greenpeace doing?

We know future sea level rise depends on what we do now. That's why Greenpeace is driving an urgent shift away from the polluting and dangerous energy systems that fuel global warming and sea level rise. We are helping make the leap to a safe, secure energy system 100 percent powered by the sun, wind, and other clean, renewable sources .

We also believe it's time to hold big carbon polluters to account , and that big polluters should contribute to making at-risk communities more resilient in the face of climate change.

More information

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Sea levels are rising because of climate change

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Sea level rise due to global warming is a serious threat, on collision course with large and growing coastal populations. For some people living in low-lying coastal areas and on small islands, damage from sea level rise is already a daily reality.

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We all associate snowstorms with cold weather, but snow's influence on the weather and climate continues long after the storm ends. Because snow is highly reflective, a vast amount of sunlight that hits the snow is reflected back into space instead of warming the planet. Without snow cover, the ground absorbs about four to six times more of the Sun's energy. The presence or absence of snow controls patterns of heating and cooling over Earth's land surface more than any other single land surface feature.

In many locations in recent decades, temperatures have risen while precipitation levels have remained largely the same. Satellite data have confirmed that average snow cover has decreased, especially in the spring and summer. Where snow cover is disappearing earlier in the spring, the large amounts of energy that would have melted the snow can now directly warm the soil.

In terms of spatial extent, seasonal snow cover is the largest single component of the cryosphere and has a mean winter maximum areal extent of 47 million square kilometers, about 98 percent of which is located in the Northern Hemisphere.

Snow cover is an important climate change variable because of its influence on energy and moisture budgets. Snow cover accounts for the large differences between summer and winter land surface albedo, both annually and inter-annually. Snow may reflect as much as 80 to 90 percent of the incoming solar energy, whereas a snow-free surface such as soil or vegetation may reflect only 10 to 20 percent. A warming trend results in decreased snow cover. With the resulting decrease in reflected energy, absorption of solar radiation increases, adding heat to the system, thereby causing even more snow to melt. This is the classic temperature-albedo feedback mechanism; it is a "positive feedback" because it reinforces itself. Surface temperature is highly dependent on the presence or absence of snow cover, and temperature trends have been linked to changes in snow cover ( Groisman et al. 1994, Brown and Robinson 2011, Peng et al. 2013).

In addition to the albedo effect, snow cover represents a significant heat sink during the melt period of the seasonal cycle due to a relatively high latent heat of fusion. As a result, the seasonal snow cover provides a major source of thermal inertia within the total climate system, as it consumes large amounts of energy with little or no fluctuation in temperature as snow crystals melt.

During the past four decades, satellite remote sensing has provided valuable information on hemispheric-scale snow extent. Since 1966, the National Oceanic and Atmospheric Administration (NOAA) has produced weekly snow extent maps for Northern Hemisphere land surfaces using visible-band satellite imagery ( Robinson and Frei 2000, Rutgers 2017). Because snow has such a high albedo compared to other surfaces on Earth, snow-covered areas appear much brighter in satellite imagery than most other surface types.

Remote sensing data sets from the microwave portion of the electromagnetic spectrum can also be used to derive snow cover maps, with the added benefit of being able to "see" through clouds. When snow covers the ground, some of the microwave energy emitted by the underlying soil is scattered by the snow grains; therefore, when moving from snow-free to snow-covered land surfaces, a sharp decrease in emissivity indicates the presence of dry snow.

These remote sensing data sets are derived using different types of analyses and separate regions of the electromagnetic spectrum, yet their results are strikingly similar. Both visible and passive microwave data sets show similar patterns of inter-annual variability, and both consistently indicate maximum snow extent that exceeds 40 million square kilometers for the Northern Hemisphere.

In the Northern Hemisphere spring (April through June), snow cover extent is mainly over the Arctic, where snow blankets the ground for up to nine months a year. The timing of springtime snow melt is particularly important in terms of spring river runoff, permafrost thaw, and the length of the growing season. Springtime snow cover extent has historically fluctuated over three- or four-year cycles, but recent observations have shown long-term snow extent declines. A study published in 2012 found an overall drop in snow cover after 1967, with an acceleration of the decline rate after 2003 ( Derksen and Brown 2012).

Recent years have shown a decreasing trend in Northern Hemisphere June snow cover extent, with most June extents since 2000 falling below the 1981-2010 average.

Long-term Northern Hemisphere snow trends are somewhat mixed, but overall show decreases in metrics such as snow cover extent, snow water equivalent, and snow depth ( Kunkel et al. 2016). Findings include a negative trend in maximum seasonal snow depth between the winter of 1960-1961 and the winter of 2014-2015. The trend is especially strong in North America, and apparent to a lesser extent in European stations discussed in the study. The authors report, "These results are mostly, but not fully, consistent with simple hypotheses for the effects of global warming on snow characteristics."

Snow totals and snow extents measured in 2015 and 2016 fit the larger pattern of declining trends. In the winter of 2015-2016, most parts of the contiguous United States showed below-average seasonal totals. The one exception was the mid-Atlantic, which received most of its snow in a single blizzard in late January 2016 ( Robinson 2016a). Throughout the Northern Hemisphere, 2016 snow cover extent ranked 12th lowest out of the 47-year average ( Robinson 2016b).

Declining snow extents are consistent with expectations for a warming climate, but another factor may also be at work. Aerosols such as dust and soot accelerate snowmelt by reducing albedo. In the San Juan Mountains of the southwestern United States, disturbed desert dust on the snow surface has affected seasonal snowpack duration. Precipitation was near average on the Colorado Plateau in 2005; the following year, the plateau experienced severe drought, and the resulting dust deposition shortened the snow-cover duration by 18 to 35 days ( Painter et al. 2007). Dust loading on the Colorado River Basin snowpack has increased fivefold since the mid-19th century, driven largely by increased land use and abuse, new dirt roadways, and agricultural practices in the region. By accelerating snowmelt, dust deposition has a significant effect on river runoff and water availability for seven U.S. states and parts of Mexico, which depend on water from the Colorado River ( Skiles et al. 2015).

Last updated: 23 February 2017

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We all associate snowstorms with cold weather, but snow's influence on the weather and climate continues long after the storm ends. Because snow is highly reflective, a vast amount of sunlight that hits the snow is reflected back into space instead of warming the planet.

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Summary of vital signs of climate change 

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Summary of vital signs of climate change 

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Climate Change: Vital Signs of the Planet

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The rate of change since the mid-20th century is unprecedented over millennia.

Earth's climate has changed throughout history. Just in the last 800,000 years, there have been eight cycles of ice ages and warmer periods, with the end of the last ice age about 11,700 years ago marking the beginning of the modern climate era - and of human civilization. Most of these climate changes are attributed to very small variations in Earth's orbit that change the amount of solar energy our planet receives.

This graph, based on the comparison of atmospheric samples contained in ice cores and more recent direct measurements, provides evidence that atmospheric CO2 has increased since the Industrial Revolution. (Credit: Luthi, D., et al.. 2008; Etheridge, D.M., et al. 2010; Vostok ice core data/J.R. Petit et al.; NOAA Mauna Loa CO2 record.) Find out more about ice cores (external site).

The current warming trend is different because it is clearly the result of human activities since the mid-1800s, and is proceeding at a rate not seen over many recent millennia. It is undeniable that human activities have produced the atmospheric gases that have trapped more of the Sun's energy in the Earth system. This extra energy has warmed the atmosphere, ocean, and land, and widespread and rapid changes in the atmosphere, ocean, cryosphere, and biosphere have occurred.

Do scientists agree on climate change?

Yes, the vast majority of actively publishing climate scientists - 97 percent - agree that humans are causing global warming and climate change.

detailed answer

Earth-orbiting satellites and new technologies have helped scientists see the big picture, collecting many different types of information about our planet and its climate all over the world. These data, collected over many years, reveal the signs and patterns of a changing climate.

Scientists demonstrated the heat-trapping nature of carbon dioxide and other gases in the mid-19th century. Many of the science instruments NASA uses to study our climate focus on how these gases affect the movement of infrared radiation through the atmosphere. From the measured impacts of increases in these gases, there is no question that increased greenhouse gas levels warm Earth in response.

"Scientific evidence for warming of the climate system is unequivocal."

- Intergovernmental Panel on Climate Change

Ice cores drawn from Greenland, Antarctica, and tropical mountain glaciers show that Earth's climate responds to changes in greenhouse gas levels. Ancient evidence can also be found in tree rings, ocean sediments, coral reefs, and layers of sedimentary rocks. This ancient, or paleoclimate, evidence reveals that current warming is occurring roughly 10 times faster than the average rate of warming after an ice age. Carbon dioxide from human activities is increasing about 250 times faster than it did from natural sources after the last Ice Age.

References

References
Header image shows clouds imitating mountains as the sun sets after midnight as seen from Denali's backcountry Unit 13 on June 14, 2019. Credit: NPS/Emily Mesner

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Climate Change Evidence: How Do We Know?

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Vital Signs of the Planet: Global Climate Change and Global Warming. How do we know it's happening? Here's the evidence.

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Quick facts, basic science, and information about snow, ice, and why the cryosphere matters

The cryosphere includes all of the snow and ice-covered regions across the planet. Explore our scientific content about what makes up this frozen realm, its importance to Earth's people, plants and animals, and what climate change means for the cryosphere and the world at large.

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Quick facts, basic science, and information about snow, ice, and why the cryosphere matters The cryosphere includes all of the snow and ice-covered regions across the planet.

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His name was Prof Bob Carter, a retired geologist speaking on behalf of the jocularly named "Non-governmental International Panel on Climate Change" (NIPCC), a ragtag band of doubting Thomases partnered with the Heartland Institute, a free-market think-tank in Chicago whose previous campaigns included working with a tobacco company to cast doubt on research linking cancer to second-hand smoke.

Carter argued that climate is always changing naturally (which is true), and that our attempts to alter its course are therefore misguided. Claiming that the NIPCC is independent, he also averred that having "around 47" contributing scientists (against the IPCC's 800-plus) made its opinions "widely held".

Reaction to Carter's performance and the BBC's decision to use him was negative. John Ashton, a Fellow at Imperial College's Grantham Institute for Climate Change, cited the 2011 report from Prof Steve Jones to the BBC Trust, in which the academic and science communicator (and Telegraph columnist) had complained of the corporation's tendency towards "false impartiality" - the "distinguished professor vs Swampy" problem. Jones had urged the BBC not to give undue prominence to individuals who give the appearance of authority but who in fact have none. Carter was such a person because he was a geologist, Ashton implied.

This conclusion, while superficially true, is also misleading. Carter may be wrong when it comes to climate science but that doesn't mean geologists, the vast majority of whom agree with the IPCC conclusions, do not have a great deal to contribute to the debate. While climatologists deal in models that predict the future - models that are always uncertain - we deal with the hard reality of the past, a past locked up in the rocks. And we have some insights into changing climates that are denied to anyone studying today's atmosphere.

Insights from the past: fossils from that era (ALAMY)

How? Well - you might think that 800,000 years - the longest interval mentioned in the IPCC report - is a long time; but it is a short and unrepresentative eye-blink in the history of the Earth (less than one 5,000th of its history), consisting mostly of glacial-interglacial cycles.

But because climate scientists only know about this tiny window on the past (albeit in incredible detail), they are fond of repeating the familiar trope that we are conducting a massive and uncontrolled experiment on the world's climate. Unfortunately, this argument implies uncertainty, and is unhelpful. There are plenty of people sowing unreasonable doubt already without climate scientists doing it to themselves.

The experiment may be massive and uncontrolled, but it is wrong to suggest we have no idea what miseries lie ahead. Ask the geologists, and they will tell you what will happen if we increase greenhouse gas concentrations by the amount we are doing now, because this has happened before. And the results then weren't pretty.

Sediment cores first taken from the Atlantic in 1997 show that 55 million years ago, over a period of about 10,000 years (coincidentally, about the same amount of time that humans have been altering climate, first by burning forests and setting brushfires, then, subtly, through agriculture and land-use changes, and in the past 200 years dramatically, by burning fossil fuels), the atmosphere was suddenly injected with carbon at about the same rate as today. And because of its isotopic composition, we know that the source was fossil - carbon that had once been in living things, just like oil and gas.

A Palaeocene/Eocene fossil from Denmark (ALAMY)

The injection was both massive and geologically sudden. Global temperatures shot up. Water close to the ocean floor rose from (an already very high) 11C (this was already a "greenhouse" world) to 15C. There was no polar ice then, so sea levels were already very elevated; but the oceans expanded as they warmed, rising by a further five to six metres, creating tropical beaches across what is now Hertfordshire. Geologists call it the "Palaeocene-Eocene Thermal Maximum" or PETM.

So what caused it? There were no humans to burn fossil fuels. Volcanic eruptions in the opening Atlantic probably kick-started the process, which ran away with itself when methane hydrates on the deep continental shelf became unstable and reverted to gas. But the cause is irrelevant; it is enough that we know the source was fossil carbon, and that in a direct mirror of modern times, sea levels rose to a degree that would displace 90 per cent of the world's present population.

Moreover, Earth did not regain equilibrium for 200,000 years - which is the time needed by natural processes to swab that amount of excess carbon dioxide out of the atmosphere. This, a near perfect analogue for today, is more enlightening than anything that has happened in the past 800,000 years, and it actually happened. The "experiment" has been run before.

Prof Bryan Lovell of Cambridge University first presented these facts for a wider readership in his book, Challenged by Carbon, in 2010. The Geological Society of London, of which he was then the president, has made many public statements and representations to Government saying the same thing.

So, get Carter by all means, but hang on to geologists. The climate change debate needs this perspective to help change minds. As Lovell is fond of saying: you can argue with geologists, you can argue with climate modellers. You can argue with climate models. But it is more than foolish to argue with a rock.

Dr Ted Nield is editor of 'Geoscientist', the monthly fellowship magazine of the Geological Society of London. His next book, 'Underlands - a Journey Through Britain's Lost Landscape', will be published by Granta in May

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Rocks hold the truth about climate change

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His name was Prof Bob Carter, a retired geologist speaking on behalf of the jocularly named "Non-governmental International Panel on Climate Change" (NIPCC), a ragtag band of doubting Thomases partnered with the Heartland Institute, a free-market think-tank in Chicago whose previous campaigns included working with a tobacco company to cast doubt on research linking cancer to second-hand smoke.

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Darwin Day Handout from Horn, Lake Sediments and Climate Change

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Slices of ice core, drilled from the depths of the Earth's ice sheets, reveal details of the planet's past climate.

Introduction

Ice cores are cylinders of ice drilled out of an ice sheet or glacier. Most ice core records come from Antarctica and Greenland, and the longest ice cores extend to 3km in depth. The oldest continuous ice core records to date extend 123,000 years in Greenland and 800,000 years in Antarctica. Ice cores contain information about past temperature, and about many other aspects of the environment. Crucially, the ice encloses small bubbles of air that contain a sample of the atmosphere - from these it is possible to measure directly the past concentration of gases (including carbon dioxide and methane) in the atmosphere.

Greenhouse gases and the recent past

Direct and continuous measurements of carbon dioxide (CO ₂) in the atmosphere extend back only to the 1950s. Ice core measurements allow us to extend this way back into the past. In an Antarctic core (Law Dome) with a very high snowfall rate, it has been possible to measure concentrations in air from as recently as the 1980s that is already enclosed in bubbles within the ice. Comparison with measurements made at South Pole station show that the ice core acts as a faithful recorder of atmospheric concentrations (see Fig. 1 overleaf), although we do have to be cautious, as artefacts can arise at sites with high concentrations of other impurities.

Antarctic ice cores show us that the concentration of CO ₂ was stable over the last millennium until the early 19th century. It then started to rise, and its concentration is now nearly 40% higher than it was before the industrial revolution (see Fig. 2 overleaf). Other measurements (e.g. isotopic data) confirm that the increase must be due to emissions of CO ₂ from fossil fuel usage and deforestation. Measurements from older ice cores (discussed below) confirm that both the magnitude and rate of the recent increase are almost certainly unprecedented over the last 800,000 years. The fastest large natural increase measured in older ice cores is around 20ppmv (parts per million by volume) in 1,000 years (a rate seen during Earth's emergence from the last ice age around 12,000 years ago). CO ₂ concentration increased by the same amount, 20ppmv, in the last 10 years! Methane (CH ₄), another important greenhouse gas, also shows a huge and unprecedented increase in concentration over the last two centuries. Its concentration is now much more than double its pre-industrial level. This is mainly due to the increase in emissions from sources such as rice fields, ruminant animals and landfills, that comes on top of natural emissions from wetlands and other sources.

Natural climate changes: glacial-interglacial cycles

By measuring the ratios of different water isotopes in polar ice cores, we can determine how temperature in Antarctica and Greenland has changed in the past. The oldest ice core we have was drilled by the European Project for Ice Coring in Antarctica (EPICA) from Dome C on the Antarctic plateau. It extends back 800,000 years and shows a succession of long, cold 'glacial' periods, interspersed roughly every 100,000 years by warm 'interglacial' periods (of which the last 11,000 years is the most recent). This succession of events is well-known from other records, and the coldest periods in Antarctica are the times when we had ice ages. Ice sheets extended over North America as far south as Wisconsin, and over Britain to south of The Wash.

The role of greenhouse gases in glacial-interglacial cycles

From the air in our oldest Antarctic ice core, we can see that CO ₂ changed in a remarkably similar way to Antarctic climate, with low concentrations during cold times, and high concentrations during warm periods (see Fig. 3 overleaf). This is entirely consistent with the idea that temperature and CO ₂ are intimately linked, and each acts to amplify changes in the other (what we call a positive feedback). It is believed that the warmings out of glacial periods are paced by changes in Earth's orbit around the Sun, but the tiny changes in climate this should cause are amplified, mainly by the resulting increase in CO ₂, and by the retreat of sea ice and ice sheets (which leads to less sunlight being reflected away). Looking at the warming out of the last glacial period in detail, we can see how remarkably closely Antarctic temperature and CO ₂ tracked each other. It is often said that the temperature 'leads' the CO ₂ during the warming out of a glacial period. On the most recent records, there is a hint that the temperature started to rise slightly (at most a few tenths of a degree) before the CO ₂, as expected if changes in Earth's orbit cause an initial small warming. But for most of the 6,000-year long 'transition', Antarctic temperature and CO ₂ rose together, consistent with the role of CO ₂ as an important amplifier of climate change (see Fig. 4 overleaf). In our modern era, of course, it is human emissions of CO ₂ that are expected to kick-start the sequence of events. We see no examples in the ice core record of a major increase in CO ₂ that was not accompanied by an increase in temperature. Methane concentration also tracks the glacial-interglacial changes, probably because there were less wetlands in the colder, drier glacial periods.

Abrupt climate changes

The climate changes described above were huge, but relatively gradual. However, ice cores have provided us with evidence that abrupt changes are also possible. During the last glacial period, Greenland experienced a sequence of very fast warmings (see Fig. 5 overleaf). The temperature increased by more than 10°C within 40 years. Other records show us that major changes in atmospheric circulation and climate were experienced all around the northern hemisphere. Antarctica and the Southern Ocean experienced a different pattern, consistent with the idea that these rapid jumps were caused by sudden changes in the transport of heat in the ocean. At this time, there was a huge ice sheet (the Laurentide) over northern North America. Freshwater delivered from the ice sheet to the North Atlantic was able periodically to disrupt the overturning of the ocean, causing the transport of tropical heat to the north to reduce and then suddenly increase again. While this mechanism cannot occur in the same way in today's world, it does show us that, at least regionally, the climate is capable of extraordinary changes within a human lifetime - rapid switches we certainly want to avoid experiencing.

Summary

Ice cores provide direct information about how greenhouse gas concentrations have changed in the past, and they also provide direct evidence that the climate can change abruptly under some circumstances. However, they provide no direct analogue for the future because the ice core era contains no periods with concentrations of CO2 comparable to those of the next century.

Factfile

Ice core. Cylinder of ice drilled out of an ice sheet or glacier. Most ice core records come from Antarctica and Greenland.

Ice cores contain information about past temperature, and about many other aspects of the environment.

Atmospheric carbon dioxide levels are now 40% higher than before the industrial revolution. This increase is due to fossil fuel usage and deforestation.

The magnitude and rate of the recent increase are almost certainly unprecedented over the last 800,000 years.

Methane also shows a huge and unprecedented increase in concentration over the last two centuries.

Data sources:

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2. Atmospheric data supplied by NOAA/ESRL

3. Friedli, H., and others: Ice core record of the 13C/12C ratio of atmospheric CO2 in the past two centuries, Nature, 324, 237-238, 1986

4. Siegenthaler, U., and others: Supporting evidence from the EPICA Dronning Maud Land ice core for atmospheric CO2 changes during the past millennium, Tellus Ser. B-Chem. Phys. Meteorol., 57, 51-57, 2005

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6. Lüthi, D., and others: High-resolution carbon dioxide concentration record 650,000-800,000 years before present, Nature, 453, 379-382, 2008

7. Monnin, E., and others: Atmospheric CO2 concentrations over the last glacial termination, Science, 291, 112-114, 2001 with data converted to the age scale of Parrenin, F., and others: The EDC3 chronology for the EPICA Dome C ice core, Climate of the Past, 3, 485-497, 2007

8. North Greenland Ice Core Project Members: High-resolution record of Northern Hemisphere climate extending into the last interglacial period, Nature, 431, 147-151, 2004

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Slices of ice core, drilled from the depths of the Earth's ice sheets, reveal details of the planet's past climate. Ice cores are cylinders of ice drilled out of an ice sheet or glacier. Most ice core records come from Antarctica and Greenland, and the longest ice cores extend to 3km in depth.

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1. Jouzel, J. and V. Masson-Delmotte, 2010. Deep ice cores: the need for going back in time. Quaternary Science Reviews, 29(27): 3683-3689. 2. Augustin, L., C. Barbante, P.R.F. Barnes, J.M. Barnola, M. Bigler, E. Castellano, O. Cattani, J. Chappellaz, D. DahlJensen, B. Delmonte, G. Dreyfus, G. Durand, S. Falourd, H.