Long-term warming likely to be significant despite recent slowdown

NASA-Goddard Space Center: A new NASA study shows Earth's climate likely will continue to warm during this century on track with previous estimates, despite the recent slowdown in the rate of global warming.

This research hinges on a new and more detailed calculation of the sensitivity of Earth's climate to the factors that cause it to change, such as greenhouse gas emissions. Drew Shindell, a climatologist at NASA's Goddard Institute for Space Studies in New York, found Earth is likely to experience roughly 20 percent more warming than estimates that were largely based on surface temperature observations during the past 150 years. Shindell's paper on this research was published March 9 in the journal Nature Climate Change.

Global temperatures have increased at a rate of 0.22 Fahrenheit (0.12 Celsius) per decade since 1951. But since 1998, the rate of warming has been only 0.09 F (0.05 C) per decade -- even as atmospheric carbon dioxide continues to rise at a rate similar to previous decades. Carbon dioxide is the most significant greenhouse gas generated by humans.

Some recent research, aimed at fine-tuning long-term warming projections by taking this slowdown into account, suggested Earth may be less sensitive to greenhouse gas increases than previously thought. The Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), which was issued in 2013 and was the consensus report on the state of climate change science, also reduced the lower range of Earth's potential for global warming.

...Shindell's paper further focuses on improving our understanding of how airborne particles, called aerosols, drive climate change in the Northern Hemisphere. Aerosols are produced by both natural sources – such as volcanoes, wildfire and sea spray – and sources such as manufacturing activities, automobiles and energy production. Depending on their make-up, some aerosols cause warming, while others create a cooling effect. In order to understand the role played by carbon dioxide emissions in global warming, it is necessary to account for the effects of atmospheric aerosols.

While multiple studies have shown the Northern Hemisphere plays a stronger role than the Southern Hemisphere in transient climate change, this had not been included in calculations of the effect of atmospheric aerosols on climate sensitivity. Prior to Shindell's work, such calculations had assumed aerosol impacts were uniform around the globe....

A new NASA study suggests that projections of Earth's future warming should be more in line with previous estimates that indicated a higher sensitivity to increasing greenhouse gas emissions. Image Credit: NASA SVS/NASA Center for Climate Simulation

Sensitivity of carbon cycle to tropical temperature variations has doubled

A press release from the University of Exeter: The tropical carbon cycle has become twice as sensitive to temperature variations over the past 50 years, new research has revealed. The research shows that a one degree rise in tropical temperature leads to around two billion extra tonnes of carbon being released per year into the atmosphere from tropical ecosystems, compared with the same tropical warming in the 1960s and 1970s.

Professor Pierre Friedlingstein and Professor Peter Cox, from the University of Exeter, collaborated with an international team of researchers from China, Germany, France and the USA, to produce the new study, which is published in the leading academic journal Nature.

Existing Earth System Model simulations indicate that the ability of tropical land ecosystems to store carbon will decline over the 21st century. However, these models are unable to capture the increase in the sensitivity of carbon dioxide to tropical temperatures that is reported in this new study.

Research published last year by Professors Cox and Friedlingstein showed that these variations in atmospheric carbon dioxide can reveal the sensitivity of tropical ecosystems to future climate change. Taken together, these studies suggest that the sensitivity of tropical ecosystems to climate change has increased substantially in recent decades.

Professor Cox, from the College of Engineering, Mathematics and Physical Sciences said: “The year-to-year variation in carbon dioxide concentration is a very useful way to monitor how tropical ecosystems are responding to climate. The increase in carbon dioxide variability in the last few decades suggests that tropical ecosystems have become more vulnerable to warming”.

Professor Friedlingstein, who is an expert in global carbon cycle studies added: “Current land carbon cycle models do not show this increase over the last 50 years, perhaps because these models underestimate emerging drought effects on tropical ecosystems”.

The lead author of the study, Xuhui Wang of Peking University, added: “This enhancement is very unlikely to have resulted from chance, and may provide a new perspective on a possible shift in the terrestrial carbon cycle over the past five decades”....

A NASA diagram of the carbon cycle