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In recent years, global warming and climate change have been the subject of a great deal of political controversy, especially in the U.S. But as the science becomes clearer and consensus grows impossible to ignore, debate is moving away from whether humans are causing warming and toward questions about how best to respond.

Temperatures rising

Evidence of rising temperatures is pervasive and striking: Thermometer records kept over the past century and a half show Earth's average temperature has risen more than 1 degree Fahrenheit (0.9 degrees Celsius), and about twice that in parts of the Arctic.

That doesn't mean temperatures haven't fluctuated among regions of the globe or between seasons and times of day. But by analyzing average temperatures all over the world, scientists have demonstrated an unmistakable upward trend.

This trend is part of climate change, which many people consider synonymous with global warming. Scientists prefer to use "climate change" when describing the complex shifts now affecting our planet's weather and climate systems. Climate change encompasses not only rising average temperatures but also extreme weather events, shifting wildlife populations and habitats, rising seas, and a range of other impacts.

All of these changes are emerging as humans continue to add heat-trapping greenhouse gases to the atmosphere.

How is climate change measured?

Although we can't look at thermometers going back thousands of years, we do have other records that help us figure out what temperatures were like in the distant past. For example, trees store information about the climate in the place they're rooted. Each year trees grow thicker and form new rings. In warmer and wetter years, the rings are thicker. Old trees and wood can tell us about conditions hundreds or even thousands of years ago.

Windows on the past are also buried in lakes and oceans. Pollen, particles, and dead creatures fall to the bottom of oceans and lakes each year, forming sediments. Sediments contain a wealth of information about what was in the air and water when they fell. Scientists reveal this record by inserting hollow tubes into the mud to collect layers of sediment going back millions of years.

For a direct look at the atmosphere of the past, scientists drill cores through the Earth's polar ice sheets. Tiny bubbles trapped in the ice are actually samples from the Earth's past atmosphere, frozen in time. That's how we know that the concentrations of greenhouse gases since the Industrial Revolution are higher than they've been for hundreds of thousands of years.

Computer models help scientists to understand the Earth's climate, or long-term weather patterns. Models also allow scientists to make predictions about the future climate by simulating how the atmosphere and oceans absorb energy from the sun and transport it around the globe.

We are the reason

Several factorsaffect how much of the sun's energy reaches Earth's surface and how much of that energy gets absorbed. Those include greenhouse gases, particles in the atmosphere (from volcanic eruptions, for example), and changes in energy coming from the sun itself.

Climate models are designed to take such factors into account. For example, models have found that changes in solar irradiance and volcanic aerosols have contributed only about two percent of the recent warming effect over 250 years. The balance comes from greenhouse gases and other human-caused factors, such as land-use changes.

The speed and duration of this recent warming is remarkable as well. Volcanic eruptions, as an example, emit particles that temporarily cool the Earth's surface. But they have no lasting effect beyond a few years. Events like El Niño also work on fairly short and predictable cycles. On the other hand, the types of global temperature fluctuations that have contributed to ice ages occur on cycles of hundreds of thousands of years.

The answer to the question, "Is global warming real?" is yes: Nothing other than the rapid rise of greenhouse gas emissions from human activity can fully explain the dramatic and relatively recent rise in global average temperatures.

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Global warming: Is it real? Get the facts.

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Scientific consensus is overwhelming: The planet is getting warmer, and humans are behind it.

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Climate change is a major issue facing the world today, but some people believe that climate change is a hoax. This term refers to the changes in temperatures and climates experienced by people living in countries all around the world. Even some famous people believe that this is an example of fake science, and others believe that it exists but not to the degree that some say. Those who deny it exists have a few key reasons for their belief.

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Their Own Experiences

One reason why some deny that climate change exists is because of their own personal experiences. Those who live in the American Midwest might point out that they still have snow and ice in the winter. As the weathers they witnessed stay the same, they assume that climate change can't exist because it would otherwise change their experiences. Those who believe in climate change point out that the seasons did change in recent years. Those living in the American Midwest may notice that winters are a little milder and that summer starts earlier and feels hotter and more humid.

No Real Proof or Evidence

According to an article by the Huffington Post, President Donald Trump told the American public that he did not believe in climate change because he didn't see any real evidence. That is a comment made by millions of other people since the 2016 election and since the American President pulled out of the Paris Accords, a pact signed by several countries to change their environmental practices. Though there is evidence out there, those who deny climate change exists refuse to look at that evidence. There are claims that any evidence that proves it exists is a type of fake science done by those who want to change public opinions.

Distrust of Science

A small number of people in the world today do not believe that climate change exists, because they do not believe in science. These people include those in fringe religious groups and sects that believe God made everyone and everything on the planet. Many of those who deny climate change exists also deny evolution and refuse to rely on some of the scientific breakthroughs that occurred in the recent past. These people represent just a small percentage of climate change deniers though.

No Known Cause

Some people claim that climate change is a hoax, because scientists cannot come to a mutual agreement on whether it exists or what causes it. While there is some evidence that climate change occurred because of human intervention such as pollution, there are other studies that dispute this claim. Deniers also claim that global warming no longer exists and that the average world temperature remained consistent for several decades. There are even claims that teachers should no longer talk about global warming in schools. Until scientists can actually find a cause for climate change and prove that it exists, many people will continue to deny that it exists.

Climate change is an important topic that people around the world cannot stop discussing. There are those who believe people should take steps to keep it from happening, but there are those who deny the idea exists. Those who think climate change is a hoax often point out the lack of evidence and proof that it even exists

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Why Do Some People Think Climate Change is a Hoax? | BestValueSchools

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Climate change is a major issue facing the world today, but some people believe that climate change is a hoax. This term refers to the changes in temperatures and climates experienced by people living in countries all around the world. Even some famous people believe that this is an example of fake science, and others ...

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For a preview of what's to come for the Earth's ecosystems, look to the past.

In a new study, an international group of researchers analyzed fossil records to track how the planet's vegetation changed as Earth climbed out of the last ice age thousands of years ago. Then, the scientists used their data to predict how vegetation in the future - and everything dependent on it - will also change. [ 6 Unexpected Effects of Climate Change]

The planet is headed into uncharted territory, with "no analog conditions" in terms of climate, said study co-author Jonathan Overpeck, the dean of the School for Environment and Sustainability at the University of Michigan. "It makes it a lot harder for us to be sure what's going to happen next."

The fossil records show that the world is very sensitive to temperature changes, which suggests that if fossil fuel emissions continue unabated, accelerated warming could lead to dramatic transformations in vegetation and ecosystems around the globe, the team wrote today (Aug. 30) in the journal Science.

Subsequently, that warming could lead to changes in the amount of carbon that plants can store, the available water supply and the global biodiversity that we depend on not only for a healthy, functioning ecosystem, but also for medicine, food and building materials, Overpeck told Live Science.

From the peak of the last ice age, 21,000 years ago, to the early Holocene epoch - the current geological age - the planet warmed by around 4 to 7 degrees Celsius (7 to 13 degrees Fahrenheit). If greenhouse gases aren't substantially reduced, the magnitude of warming that occurred over the course of 11,000 years following the end of the ice age will happen over a much shorter period: 100 to 150 years.

Rewinding the tape

To decipher how plant life changed in the past, the researchers analyzed ancient pollen and plant fossils from nearly 600 sites on every continent except Antarctica. The investigators divided the changes they observed into two categories: compositional changes, or changes in plant species in the area, and large structural changes, like a tundra becoming a forest or a deciduous forest becoming an evergreen forest. The various changes were classified as "large," "moderate" or "low."

Then, focusing on the sites with moderate or large changes, the scientists further classified the sites, this time addressing the role climate change could have played in the shifts. They used the same scale for the role of climate (low, moderate or large). In other words, the researchers sought to determine whether the large changes were due to climate change or the result of, for example, human activity or large animals.

The researchers found that the warming period after the last ice age played a large role in vegetation changes around the world. Areas that had the greatest temperature changes also tended to be those with the greatest vegetation changes, the study showed.

(Image credit: Nolan et al., Science (2018))

Indeed, the scientists found that warming temperatures largely changed the composition of the vegetation in 71 percent of the sites around the world and the structure of the vegetation in 67 percent of the sites; rising temperatures moderately changed the composition in another 27 percent of the sites and the structure in 28 percent of the sites.

The changes in plant life were most evident in mid to high latitudes in the Northern Hemisphere, as well as in southern South America, tropical and temperate southern Africa, the Indo-Pacific region, Australia, New Zealand and other countries in Oceania.

There were also some sites that showed very little compositional or structural change in vegetation, according to the paper. But nearly all sites with low compositional change also experienced low temperature changes.

This shows that our planet is highly sensitive to temperature changes, Overpeck said. Even if we end up curbing fossil fuel emissions and meeting the targets of the Paris Agreement, some change is still inevitable, but it would affect less than half the planet, he said.

In contrast, if we don't meet the Paris targets, "then we'll have much wider change around the planet." And that change will be much bigger and more difficult to predict.

Underestimating change

Peter Verburg, a professor of environmental geography at the University of Amsterdam who was not part of the research, said that it's difficult to extrapolate the study's findings to the present day.

The study was "based on paleo[lithic] conditions, and the present-day vegetation is incomparable [to the vegetation in those conditions] as human activities have changed land cover in some way in about 80 percent of the terrestrial surface," Verburg told Live Science in an email.

"Nevertheless, what we learn is that ecosystems are extremely sensitive to changes in climate," he said.

Indeed, the new study is "another confirmation that climate change will hugely affect the Earth system and the ecosystems we depend on," Verburg said. In other words, it is yet "another call for immediate action."

Overpeck said that the results of this study likely underestimate the change that will happen in the future if we don't curb emissions.

"There are many reasons why these forests are going to have a rougher time [adapting to climate change] in the future than they had in the past," Overpeck said, but perhaps the major reason is that the time frame is sped up so significantly. That makes it a lot harder for the ecosystem to adjust.

And we're already seeing some changes in plant life today, Overpeck said. The warming of the planet is creating dryer ecosystems in certain parts of the world, like the western U.S., Australia and Eurasia. "So what we're seeing in the western [U.S.] are whole regions of increased tree death because of warming and drying," he said.

"We are also seeing a big uptick in insect and disease in forests because these trees are being weakened by the warming," he added.

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Climate Change Could Drastically Change Ecosystems Around the World

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For a preview of what's to come for the Earth's ecosystems, look to the past. In a new study, an international group of researchers analyzed fossil records to track how the planet's vegetation changed as Earth climbed out of the last ice age thousands of years ago.