By testing whether human activities like deforestation and pollution pose a risk to the climate, scientists have identified an unexpected potential climate response that could explain the warming of the planet.
In an experiment designed to measure the response of global warming to CO2, scientists used an air pollutant called nitrogen oxides (NOx).
Nitrogen oxides are a natural component of the atmosphere that can react with atmospheric nitrogen to form CO2.
They are the principal greenhouse gas that is released when CO2 emissions rise in response to human activity.
Scientists used a technique known as climate prediction, which combines a computer model with the measurement of natural processes, to assess how well the climate responds to CO02.
This is the first study to test the response to CO 2.
The team of scientists used computer simulations of a large-scale system that is currently operating in Antarctica to study the response.
The system uses the global ocean circulation to change ocean temperature and sea level.
The simulation is part of a climate model known as the Southern Ocean Oscillation (SOO) that has been widely used to forecast climate in the past.
“We’ve used a large ensemble of model simulations to simulate climate across the Southern Oscillator,” said study co-author Chris Bell, an atmospheric scientist at the University of Bristol.
“We’re trying to understand how the system responds to changes in CO2 and how that changes the climate.”
The team’s simulations revealed that when the SOO system changes to include more CO2 than normal, the system begins to warm.
In contrast, when the system is in the state of neutrality, the atmosphere stays at a similar temperature to the surrounding atmosphere, and the climate is cooler than normal.
This warm-to-cool response to rising CO2 is not found in any of the other climate models currently used to predict the response, but it is the result of the response being caused by an increased concentration of CO2 in the atmosphere.
“There is a huge difference between these two responses,” said co-lead author Andrew Weisberg, an assistant professor of physics at the Massachusetts Institute of Technology (MIT).
“If we had a neutral climate in which we were using a normal climate model, the response would be the same.”
“The difference between the two responses is that in the case of the SOOC, the effect of the CO2 on the atmosphere is much smaller than the effect on the surface,” said lead author Peter J. Hotez, an associate professor of atmospheric science at the California Institute of Tech.
“But the effect is much bigger when the CO 2 is in neutral.”
In other words, the warming that occurs when the ocean circulates more strongly in response that the response caused by human activities can be used to tell the climate about the effects of CO 2 on the climate.
“It’s a pretty powerful demonstration that CO2 has a role to play in the climate,” said Bell.
“If you think about it in the context of what we see happening in the surface temperature, there’s probably a mechanism in the system that would be able to explain how the surface is changing.”
Bell said the CO₂-enhanced response could be due to feedbacks, such as changes in the chemistry of the oceans and the ocean’s response to increased CO2 concentrations.
This feedback would also be part of the overall feedback mechanism, which could explain why the surface of the Earth is warming, even if the ocean is not warming.
“The feedback mechanism that we’re seeing is a very interesting one, because it’s one that’s difficult to explain using just the physical properties of COℂ,” said Weis, who is a member of the climate modeling team at the Carnegie Institution of Washington.
The research was published in the journal Nature Climate Change.