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"Do you believe in Climate Change?" we have all heard that question, what I want to know are your thoughts about climate change. What does the idea of a changing climate mean to you? Is it something we can "believe" in? What do you think about climate change?

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It's Not your Imagination.  Summers Are Getting Hotter

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It's Not your Imagination.  Summers Are Getting Hotter

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By NADJA POPOVICH and ADAM PEARCE JULY 28, 2017

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Extraordinarily hot summers - the kind that were virtually unheard-of in the 1950s - have become commonplace.

This year's scorching summer events, like heat waves rolling through southern Europe and temperatures nearing 130 degrees Fahrenheit in Pakistan, are part of this broader trend.

The chart above, based on data from James Hansen, a retired NASA climate scientist and professor at Columbia University, shows how summer temperatures have shifted toward more extreme heat over the past several decades.

To create the bell curves, Dr. Hansen and two colleagues compared actual summer temperatures for each decade since the 1980s to a fixed baseline average. During the base period, 1951 to 1980, about a third of local summer temperatures across the Northern Hemisphere were in what they called a "near average" or normal range. A third were considered cold; a third were hot.

Since then, summer temperatures have shifted drastically, the researchers found. Between 2005 and 2015, two-thirds of values were in the hot category, and nearly 15 percent were in a new category: extremely hot.

Practically, that means most summers are now either hot or extremely hot compared with the mid-20th century.

The big increase in summer temperatures under the dark red category of extreme heat is "right in line" with what scientists expect to see as the climate warms over all, said Todd Sanford, director of research at Climate Central, a nonprofit science and news organization.

For each time period above, the distribution of summer temperatures forms what is known as a bell curve because most measurements fall near the average, forming the bump - or bell - in the middle. More extreme temperatures, which happen less frequently, fall in the wings, with heat waves on the right and cold-snaps on the left.

As the curve's average - the top of the peak - shifts rightward over time, more temperatures in more places end up in the hot and extremely hot categories and fewer end up in the cold category.

Dr. Hansen's curves also flatten out, which some have suggested is an indication of greater temperature variability. But other climate scientists, including Zeke Hausfather, an energy systems analyst at the University of California, Berkeley, have pointed out that this effect is mainly a reflection that some parts of the world are warming faster than others. There is no evidence that temperatures are becoming more variable in most parts of the world after warming has been accounted for.

Dr. Hansen's data "really highlight that changes in the average, while they may seem modest, have big implications for the extremes. And that's what's going to affect society and ecosystems," Dr. Sanford said. The findings reveal what has happened so far, and also provide "a glimpse to what's in our future."

Temperature categories are determined by the normal distribution, so that a third of temperatures fall in each of the main three categories: hot, cold and normal for 1951 to 1980. Summer temperatures for each subsequent 11-year period are compared to the 1951 to 1980 baseline.

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It's Not Your Imagination. Summers Are Getting Hotter.

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Extraordinarily hot summers - the kind that were virtually unheard-of in the 1950s - have become commonplace. This year's scorching summer events, like heat waves rolling through southern Europe and temperatures nearing 130 degrees Fahrenheit in Pakistan, are part of this broader trend.

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NASA and NWS

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Climate Change: Vital Signs of the Planet

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Carbon dioxide (CO ₂) is an important heat-trapping gas, also known as a greenhouse gas, that comes from the extraction and burning of fossil fuels (such as coal, oil, and natural gas), from wildfires, and natural processes like volcanic eruptions. The first graph shows atmospheric CO ₂ levels measured by NOAA at Mauna Loa Observatory, Hawaii, since 1958. The second graph shows CO ₂ levels during Earth's last three glacial cycles, as captured by air bubbles trapped in ice sheets and glaciers.

Since the onset of industrial times in the 18th century, human activities have raised atmospheric CO ₂ by 50% - meaning the amount of CO ₂ is now 150% of its value in 1750. This human-induced rise is greater than the natural increase observed at the end of the last ice age 20,000 years ago.

The animated map shows how the historical changes in global carbon dioxide over time. Note the colors change as the amount of CO ₂ rises from 365 parts per million (ppm) in 2002 to over 420 ppm currently. It's important to understand that "parts per million" refers to the number of carbon dioxide molecules per million molecules of dry air. These measurements are from the mid-troposphere, the layer of Earth's atmosphere that is 8 to 12 kilometers (about 5 to 7 miles) above the ground. This data provides insights into the significant rise in atmospheric CO2 concentrations, highlighting the impact of human activities on Earth's climate.

CO₂ Through the Seasons

A closer look at the carbon dioxide measurements at Mauna Loa shows a series of wiggles in the data. Although total CO ₂ is increasing each year, there is also a short-term cycle visible within the larger trend.

This annual rise and fall of CO ₂ levels is caused by seasonal cycles in photosynthesis on a massive scale. In Northern Hemisphere spring, plants come to life and draw in CO ₂ to fuel their growth. This begins the process of lowering the amount of CO ₂ in the atmosphere. In northern autumn, plant growth stops or slows down, and the whole process reverses itself. Much of the plant matter decomposes, releasing CO ₂ back to the atmosphere.

A similar but less intense pattern repeats in the Southern Hemisphere in opposite seasons. Spring growth starts in September and winter decomposition begins in March, so CO ₂ records in the Southern Hemisphere show the opposite pattern of that seen in Mauna Loa. However, because there is a lot more land and vegetation in the Northern Hemisphere than the southern, the global seasonal cycle more closely aligns with the northern pattern.

See the cycle in action in the visualization Watching Earth Breathe: The Seasonal Vegetation Cycle and Atmospheric Carbon Dioxide.

This boom-and-bust cycle of plant growth gives the graph of CO ₂ a sawtooth pattern of ups and downs from year to year. At a larger scale, the upward climb of the trend line over the decades is caused by CO ₂ emissions, primarily from burning fossil fuels. Thus, the data illustrate both natural factors and human additions of CO ₂.

Learn more:

NASA's Climate Kids: Why is Carbon Important?

Missions That Observe CO₂
Atmospheric Infrared Sounder (AIRS) Orbiting Carbon Observatory (OCO-2) Orbiting Carbon Observatory (OCO-3)

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Carbon Dioxide Concentration | NASA Global Climate Change

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Vital Signs of the Planet: Global Climate Change and Global Warming. Current news and data streams about global warming and climate change from NASA.

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Climate change_ Earth's giant game of Tetris - Joss Fong

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In the new video above, Bill Nye the Science Guy explains why climate change is much more than a buzzword. "It's a real and serious issue," he says.

In fact, the world's leaders are debating what to do about it this week in Paris. It's true Earth's climate has changed through time naturally due to slight changes in the planet's orbit, Nye notes, "but climate change as we know it today is characterized by an abrupt increase in the Earth's temperature."

That's 1.2 to 1.4 degrees Fahrenheit warmer over the past century. Ten of the last 13 years were the warmest on record (including this year, according to a recent report). And 97 percent of climate scientists think this warming has been caused by human activity, Nye says.

More on Paris Climate Talks

"That means you, and me," he says, thanks to all the things we do that result in more greenhouse gases in the atmosphere. Those gases keep more of the sun's heat trapped near the surface, resulting in rising temperatures, a warming ocean, rising sea levels, and more natural disasters.

Although the effects of climate change are threatening, "scientists still believe there are things we can do on a personal level to help," says Nye. Those strategies include recycling and reusing things, walking and using public transit, turning off unused appliances, and eating less meat.

"When it comes to climate change, the main takeaway is it's real," says Nye. "And although we are part of the problem, we can also be part of the solution."

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Bill Nye Tells You What You Need to Know About Climate Change

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In the new video above, Bill Nye the Science Guy explains why climate change is much more than a buzzword. "It's a real and serious issue," he says. In fact, the world's leaders are debating what to do about it this week in Paris.