Environmentalists have long argued the burning of fossil fuels in power stations and for other uses is responsible for global warming and predicted temperature increases because of the high levels of carbon dioxide produced – which causes the global greenhouse effect.
While the findings did not dispute the effects of carbon dioxide on global warming, they found aerosols – also given off by burning fossil fuels – actually cool the local environment, at least temporarily.
The research was carried out to see if current climate change models for calculating future temperatures were taking into account all factors and were accurate.
A NASA spokesman said: “To quantify climate change, researchers need to know the Transient Climate Response (TCR) and Equilibrium Climate Sensitivity (ECS) of Earth.
On December 7, NASA’s Aqua satellite captured this image of eastern China being inundated by smog.
“TCR is characteristic of short-term predictions, up to a century out, while ECS looks centuries further into the future, when the entire climate system has reached equilibrium and temperatures have stabilised.”
The spokesman said it was “well known” that aerosols such as those emitted in volcanic eruptions and power stations, act to cool Earth, at least temporarily, by reflecting solar radiation away from the planet.
He added: “In a similar fashion, land use changes such as deforestation in northern latitudes result in bare land that increases reflected sunlight.”
Kate Marvel, a climatologist at GISS and the paper’s lead author, said the results showed the “complexity” of estimating future global temperatures.
She said: “Take sulfate aerosols, which are created from burning fossil fuels and contribute to atmospheric cooling.
“They are more or less confined to the northern hemisphere, where most of us live and emit pollution.
NASA found a net cooling in the northern hemisphere due to industrial activity.
Take sulfate aerosols, which are created from burning fossil fuels and contribute to atmospheric cooling. They are more or less confined to the northern hemisphere, where most of us live and emit pollution
“Because earlier studies do not account for what amounts to a net cooling effect for parts of the northern hemisphere, predictions for TCR and ECS have been lower than they should be.”
The study found existing models for climate change had been too simplistic and did not account for these factors.
The spokesman said: “There have been many attempts to determine TCR and ECS values based on the history of temperature changes over the last 150 years and the measurements of important climate drivers, such as carbon dioxide.
“As part of that calculation, researchers have relied on simplifying assumptions when accounting for the temperature impacts of climate drivers other than carbon dioxide, such as tiny particles in the atmosphere known as aerosols, for example.
Climate scientist Gavin Schmidt, the director of NASA’s Goddard Institute for Space Studies (GISS) in New York and a co-author on the study, published in the journal Nature Climate Change, said: “The assumptions made to account for these drivers are too simplistic and result in incorrect estimates of TCR and ECS.
“The problem with that approach is that it falls way short of capturing the individual regional impacts of each of those variables,” he said, adding that only within the last ten years has there been enough available data on aerosols to abandon the simple assumption and instead attempt detailed calculations.
But, rather than being good news, NASA has concluded the lack of taking these factors into account means existing climate change models have underestimated at the future impact on global temperatures will be.
NASA looked at climate changing activities across the globe for the study
The spokesman said: “Analysis of the results showed that these climate drivers do not necessarily behave like carbon dioxide, which is uniformly spread throughout the globe and produces a consistent temperature response; rather, each climate driver has a particular set of conditions that affects the temperature response of Earth.
“Because earlier studies do not account for what amounts to a net cooling effect for parts of the northern hemisphere, predictions for TCR and ECS have been lower than they should be.
“This means that Earth’s climate sensitivity to carbon dioxide—or atmospheric carbon dioxide’s capacity to affect temperature change—has been underestimated, according to the study.”
The Intergovernmental Panel on Climate Change, which draws its TCR estimate from earlier research, places the future estimate rise at 1.8°F (1.0°C).
But the new NASA study dovetails with a GISS study published last year that puts the TCR value at 3.0°F (1.7° C).
Mr Schmidt said: “If you’ve got a systematic underestimate of what the greenhouse gas-driven change would be, then you’re systematically underestimating what’s going to happen in the future when greenhouse gases are by far the dominant climate driver.”