NASA measures direct evidence that humans are causing climate change

This may come as a surprise, given the vast body of evidence linking humans to climate change, this directly observed evidence of human impact on the climate was still elusive of science. That is, until now.

In a one-of-a-kind study, NASA calculated the individual driving forces of recent climate change through direct satellite observations. And according to what climate models have shown for decades, greenhouse gases and airborne pollution particles called aerosols from the burning of fossil fuels are responsible for the lion’s share of the world. modern warming.

In other words, NASA has proven what causes climate change through direct observations – a gold standard in scientific research.

“I think most people would be surprised if we haven’t yet filled this little gap in our long list of supporting evidence. [human-caused] climate change, ”says Brian Soden, study co-author and professor of atmospheric science at the Rosenstiel School of Marine and Atmospheric Science at the University of Miami.

Now it is common knowledge that the rapid warming up of the last century is not natural. Rather, it is the result of the build-up of heat-trapping greenhouse gases like carbon dioxide (CO2) and methane, largely Burning of fossil fuels.

The science behind global warming

When sunlight enters the atmosphere, some of it is sent back into space without heating the Earth. The rest is absorbed by the Earth’s surface and atmosphere and re-emitted as heat. Some of this heat escapes into space, but the rest of the heat is trapped by specific molecules like CO2, methane, and water vapor. Simply, the more greenhouse gases in the atmosphere, the more heat is trapped and the more the temperature rises.

Since the mid-1800s, CO2 in the atmosphere rose from 280 parts per million to 415 parts per million – a 50% increase – and it is now the highest for at least 3 million years. Carbon dioxide in the atmosphere is increasing at a rate 100 times faster than it should naturally.

At the same time, airborne pollution particles, called aerosols, cool the atmosphere by blocking sunlight. This unintended side effect of the industrial revolution has proven to be useful in masking greenhouse warming.

Although these particles were effective in counteracting some of the global warming in the mid to late 20th century, their impact is diminishing, as since the 1980s pollution has gradually dissipated. While this is great health news, it does unmask further warming in the system.

Together, the change in heat absorbed into our atmosphere due to changes in greenhouse gases and aerosols is called “radiative forcing.” These changes in radiative forcing disrupt the Earth’s energy balance. This is because, in order for Earth’s average temperatures to remain stable, the sun’s “energy input” must be matched by Earth’s “energy output” to space.

When these numbers are equal, the Earth maintains balance. But when greenhouse gases build up, the energy coming out is less than the energy entering the Earth system, which warms our oceans and atmosphere, creating an imbalance in Earth’s energy budget.

What NASA did in this study is calculate or quantify the individual forcings measured from specialized satellite observations to determine how well each component warms or cools the atmosphere. Unsurprisingly, what they found was that the radiative forces, which computer models have been showing for decades warming the Earth, correspond to the changes they measure in observations.

New insight from NASA

Gavin Schmidt, director of the Goddard Institute for Space Studies at NASA, says science has long had an overwhelming amount of circumstantial evidence of the factors warming the Earth. The predicted energy imbalance illustrated by decades of computer models has become apparent for all of humanity to see, from disappearance of glaciers see you extreme weather disasters at ocean warming.

“We have long had good evidence that the predicted energy imbalance was real due to the increasing heat content of the oceans. This is a very powerful confirmation that the models were predicting warming for the right reasons, ”says Schmidt. He says scientists also had direct evidence that changes in greenhouse gases affected heat transfer and absorption in the atmosphere, but only in localized settings, not a full assessment.

Soden adds that science has strong observational evidence that CO2 has increased over the past century due to the combustion of greenhouse gases and that laboratory measurements confirm that CO2 absorbs heat, which should theoretically cause the planet to warm at about the rate observed in the last. century. However, Soden says observing the heat trapping of space is actually quite difficult. This new research solves that challenge.

“This is the first calculation of Earth’s total radiative forcing using global observations, taking into account the effects of aerosols and greenhouse gases,” said Ryan Kramer, lead author of the article. and researcher at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. . “This is direct evidence that human activities are causing changes in the Earth’s energy budget.”

Specifically, this study was able to calculate solid numbers for changes in trapped heat in the Earth system from the various contributors that influence heat transfer, such as radiation, clouds, and water vapor. , for the period 2003-2019. The researchers did this by analyzing satellite observations and applying what they call “radiative nuclei” to unravel the various components controlling the transfer, absorption and emission of heat within the Earth system. which is sent back into space. Until then, satellite observations of the Earth’s radiation budget had measured only the sum total of radiation changes, not the individual components.

Then there are also feedbacks in the climate system that explain a smaller but still significant warming. An example of this is the fact that, as the atmosphere warms up, it can hold more water vapor, which means it can trap more heat, further allowing more vapor to drip. water to accumulate. It’s positive feedback that keeps warming going.

The result: From 2003 to 2018, radiative forcing increased by 0.5 watts per square meter (W / m2), which explains the planetary imbalance, the excess heat trapped in the Earth system. The researchers conclude that this increase is indeed due to a combination of mainly increasing concentrations of greenhouse gases and, to a lesser extent, recent reductions in aerosol emissions.

For reference, Schmidt says that the excess 0.5 W / m2 added to the Earth system from 2003 to 2018 is roughly equivalent to one Christmas tree light bulb for every 5 square foot area on Earth. That may not sound like a lot, but this amount of energy is expected to warm the planet by over half a degree Fahrenheit in just 16 years. To put it another way, the 0.5 W / m2 of excess heat absorbed by the Earth system is 10 times the total energy used by humans in a year, that is, everything from stoves to energy. nuclear.

“In fact, the observation results arrived exactly as theoretically expected,” Soden explains. “There is no surprise in the results, but rather it is a matter of” sprinkling the i’s and crossing the t’s “on the [human-caused] climate change. It closes this last link between rising CO2 levels and global warming. “

But this study does more than just provide concrete evidence of the link between humans and recent climate change. It also illustrates how far science has come to uncover the secrets that govern how our physical universe works.