This may come as a surprise, given the vast body of evidence that connects people climate change, the direct observed evidence of human impact on the climate, science has still eluded. That is, until now.
In a first-of-its-kind study, NASA calculated the individual drivers of recent climate change using direct satellite observations. And according to what climate models have been showing for decades, greenhouse gases and suspended pollutants in the atmosphere, called aerosols, are responsible for most of modern heating through the combustion of fossil fuels.
In other words, NASA has proven what drives climate change through direct observations – a gold standard in scientific research.
‘I think most people would be surprised that we have not yet closed this small gap in our long list of evidence that supports anthropogenic [human-caused] climate change, ”says Brian Soden, co-author of the study and professor of atmospheric science at the Rosenstiel School of Marine and Atmospheric Science at the University of Miami.
By this time it is common knowledge that the rapid warm-up of the last century is not of course. Rather, it is a result of the build-up of greenhouse gases such as carbon dioxide (CO2) and methane that capture heat, many of which combustion of fossil fuels.
The science behind why the earth is warming
When sunlight enters the atmosphere, it is reflected back into space without heating the earth. The rest is absorbed by the earth’s surface and atmosphere and radiated again as heat. Some of this heat escapes back into space, but the rest of the heat is trapped by specific molecules such as CO2, methane and water vapor. The more greenhouse gases the atmosphere has, the more heat is trapped and the more the temperature rises.
NASA
Since the mid-1800s, CO2 in the atmosphere has increased from 280 parts per million to 415 parts per million – an increase of 50% – and it is now the highest it has been in at least 3 million years. Carbon dioxide in the atmosphere increases 100 times faster than it naturally should.
At the same time, suspended pollutant particles, called aerosols, cool the atmosphere by blocking sunlight. This unintended side effect of the Industrial Revolution is useful in disguising greenhouse heating.
Although these particles could effectively help counteract some of global warming in the mid to late 20th century, their impact is diminishing as pollution is gradually cleared up. While this is good news for health, it exposes extra heat in the system.
Together, the change in heat absorbed into our atmosphere due to changes in greenhouse gases and aerosols is called ‘radiation coercion’. These changes in the radiative forcing impede the earth’s energy balance. This is because the ‘energy-in’ of the sun must be equalized by the ‘energy-out’ of the earth to the earth, so that the average temperature of the earth can remain constant.
If the numbers are equal, the earth maintains the balance. But when greenhouse gases build up, the energy that goes out is less than the energy that enters the Earth system, which warms our oceans and atmosphere, which creates an imbalance in the Earth’s energy budget.
What NASA did in this study is to calculate or quantify the individual forces, measured by specialized satellite observations, to determine how much each component warms or cools the atmosphere. To no one’s surprise, they find that the radiating forces, which computer models have been indicating for decades, are warming the earth are consistent with the changes they are measuring in observations.
New insight from NASA
Gavin Schmidt, director of the NASA Goddard Institute for Space Studies, says science has long had an overwhelming amount of indirect evidence of the factors warming the Earth. The predicted energy imbalance illustrated by computer models for decades has become clear to all mankind disappearing glaciers to more extreme weather disasters on warm oceans.
“We have long had good evidence that the predicted energy imbalance was real due to the increase in ocean heat content. It is a very powerful confirmation that the models predicted the right reasons for warming,” explains Schmidt. He says scientists also had direct evidence that changes in greenhouse gases affected the transfer and absorption of heat into the atmosphere, but only in the local environment, not a comprehensive evaluation.
Soden adds that science does have solid observational evidence that CO2 has increased over the past century due to the burning of greenhouse gases, and that laboratory measurements confirm that CO2 absorbs heat, which should theoretically cause the planet to warm up at about the rate observed. century. However, Soden says observing the capture of heat from space is actually quite challenging. This new research solves the challenge.
“This is the first calculation of the Earth’s total radiative forcing using global observations, taking into account the effects of aerosols and greenhouse gases,” said Ryan Kramer, first author on paper, and a researcher at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said. . “This is direct evidence that human activity is causing changes in the Earth’s energy budget.”
This study was able to specifically calculate solid numbers for the changes in heat trapped in the Earth system, of the individual contributors affecting 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 ‘radiation cores’ to disrupt the various components that control the transmission, absorption and emission of heat within the Earth’s system, and which are sent back into space. Up to this point, satellite observations of the Earth’s radiation budget have only measured the sum total of the radiation changes, not the individual components.
Then there is also feedback in the climate system that accounts for a smaller but still significant amount of warming. One example of this is the fact that the atmosphere can contain more water vapor when the atmosphere gets hot, and this means that it can trap more heat, which can further build up more water vapor. This is a positive feedback that the heating continues.
The result: From 2003 to 2018, radiant power increased by 0.5 watts per square meter (W / m2), which is responsible for the planetary imbalance, the excess heat trapped in the earth’s system. The researchers conclude that this increase was indeed due to a combination of mainly rising 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 2003-2018 is approximately equal to one Christmas tree light bulb for every surface of 5 feet on earth. It may not sound like much, but it is expected that there will be so much energy warming the planet with more than half a degree Fahrenheit within 15 years. In other words: the 0.5 W / m2 excess heat absorbed by the Earth’s system is ten times the total energy that man uses in a year, which means everything from stoves to nuclear power.
“In fact, the observational results came just as the theory predicted,” Soden says. “There is no surprise in the results, but rather ‘to dot the i’s and cross the t’s’ on anthropogenic [human-caused] climate change. This includes the last link between rising CO2 levels and planetary warming. ‘
But this study provides more than just concrete evidence of the link between humans and recent climate change. It also illustrates how far science has come in discovering the secrets that control the functioning of our physical universe.