It may come as a surprise, given the extensive evidence that connects humans climate change, directly observed evidence of human impact on the climate had still eluded science. That is, so far.
In a first study of this type, NASA has calculated the individual driving forces of recent climate change through direct satellite observations. And, according to climate models for decades, greenhouse gases and airborne pollution particles, called aerosols, derived from the combustion of fossil fuels are responsible for most of the lion in modern warming.
In other words, NASA has shown what is driving climate change through direct observations, a gold standard in scientific research.
“I think most people would be surprised if we hadn’t closed that little gap in our long list of evidence supporting anthropogenesis yet. [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 School at the University of Miami.
By now you know that rapid heating of the last century is not natural. Rather, it is the result of the accumulation of greenhouse gases that capture heat such as carbon dioxide (CO2) and methane, much of the combustion of fossil fuels.
The science behind why the Earth is warming
When sunlight enters the atmosphere, part of it is reflected into space without heating the Earth. The rest is absorbed by the Earth’s surface and atmosphere and radiates again as heat. Part 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. Simply put, the more greenhouse gases the atmosphere has, the more heat gets trapped and the higher the temperature.
NASA
Since the mid-1800s, CO2 in the atmosphere it has gone from 280 parts per million to 415 parts per million (50% more) and is now the highest it has been in at least 3 million years. Carbon dioxide in the atmosphere increases at a rate 100 times faster than it should naturally.
At the same time, suspended pollution particles, called aerosols, cool the atmosphere by blocking sunlight. This unintended side effect of the Industrial Revolution has been shown to be useful in masking some greenhouse warming.
Although these particles were effective in helping to counteract some of global warming in the mid to late 20th century, their impact is waning, as pollution has been gradually reduced since the 1980s. While it’s great news for health, it’s unmasking an additional warm-up in the system.
Altogether, the change in heat absorbed into our atmosphere due to changes in greenhouse gases and aerosols is called “radiative forcing”. These changes in radiative force trigger the Earth’s energy balance. This is because, for the average temperatures of the Earth to remain constant, the “energy input” of the sun must be equaled by the “energy output” of the Earth into space.
When these numbers are equal, the Earth maintains balance. But when greenhouse gases accumulate, the energy that comes out is less than the energy that goes into the Earth’s system, which heats our oceans and atmosphere, creating an imbalance in the Earth’s energy budget.
What NASA has done in this study is to calculate or quantify the individual forces measured from specialized satellite observations to determine how much each component heats or cools the atmosphere. For no one, what they have discovered is that radiative forces, which computer models have indicated for decades, were warming the Earth, coincide with the changes they measure in observations.
New vision of NASA
Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies, says science has long had an overwhelming amount of indirect evidence of the factors that warm the Earth. The predicted energy imbalance illustrated by the value of decades of computer models has become apparent to all of humanity disappearing glaciers Besides extreme weather disasters a warming of the oceans.
“We have long had good evidence that the predicted energy imbalance was real due to increases in ocean heat content. This is a very powerful confirmation that the models predict warming for the right reasons,” Schmidt explains. He says scientists have also had direct evidence that changes in greenhouse gases have affected heat transfer and absorption into the atmosphere, but only in localized environments, not a full assessment.
Soden adds that science has solid 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 in theory it should. that the planet warms at approximately the speed observed in recent years. century. Still, Soden says observing heat capture from space is really quite difficult. This new research solves this 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, lead author of the paper and researcher at the Goddard Space Flight Center. NASA in Greenbelt, Maryland. . “It is direct evidence that human activities are causing changes in the Earth’s energy budget.”
Specifically, this study has been able to calculate solid numbers for heat changes trapped in the Earth’s system from individual contributors influencing heat transfer, such as radiation, clouds, and water vapor, for the 2003 period. -2019. The researchers did this by analyzing the observations of the satellites and applying what they call “radiative nuclei” to untangle the different components that control the transfer, absorption and emission of heat inside the Earth’s system and what is sent into space. Until then, satellite observations of the Earth’s radiation budget had only measured the total sum of radiation changes, not the individual components.
In addition, there are also feedbacks in the climate system that explain a smaller but still significant amount of warming. An example of this is the fact that as the atmosphere heats up, it can contain more water vapor and this means it can trap more heat, which allows more water vapor to accumulate. This is positive feedback that perpetuates warming.
The result: from 2003 to 2018, radiative forcing has increased 0.5 watts per square meter (W / m2), which explains the planetary imbalance, the excess heat trapped in the Earth’s system. The researchers conclude that this increase was due, in fact, to a combination of mostly increasing concentrations of greenhouse gases and, to a lesser extent, to recent reductions in aerosol emissions.
As a reference, Schmidt says the excess of 0.5 W / m2 added to the Earth system from 2003 to 2018 is roughly equivalent to one Christmas tree bulb for every 5 square feet of area on Earth. This may not sound like much, but it is expected that so much energy will heat the planet more than half a degree Fahrenheit in just 16 years. In other words, the 0.5 W / m2 of excess heat absorbed by the Earth’s system is 10 times the total energy that humans make in a year, that is, from stoves to energy nuclear.
“Actually, the observational results came as the theory predicted,” Soden says. “There is no surprise in the results, but it is rather‘ punctuating the ii crossing the ’in anthropogenic. [human-caused] climate change. It closes the latter link between rising CO2 levels and global warming. “
But this study not only provides concrete evidence of the link between humans and recent climate change. It also illustrates the extent to which science has come to discover the secrets that govern the functioning of our physical universe.