In their efforts to deny man made climate change, skeptics have frequently pointed to a pause in rising global temperatures to try to dissuade from the seriousness of the global warming threat. Now, scientists think they know exactly what caused that pause and it’s good news: we did!
A new study, published in the journal Nature Geoscience, shines a light on the intriguing fact that since 1998, global temperature rises seem to have paused. Researchers from the Institute for Environmental Studies in Amsterdam, the Netherlands, used a new statistical analysis on temperature rise and the atmosphere’s greenhouse gas concentrations between 1880-2010 as part of a wider study into human influence over climate temperatures.
What they found was that when humans have intervened to lower global emissions, there appears to have been a pause in global warming.
For instance, the pause in rising global temperatures in the late 1990s appears to have been at least partly as a result of the signing of the Montreal Protocol in 1987, where 46 world powers agreed to a reduction in the emission of ozone-depleting chemicals known as CFCs, as well as a cut in methane emissions. While CFCs are known to have thinned the ozone layer, they also are many times more powerful than CO2 as insulating gasses and linger in the atmosphere for much longer.
This is one of several examples the scientists have identified where global temperature increase stalled as a result of human efforts to reduce emissions.
Other examples the study points to include the reduction of CO2 output during both world wars and during the Great Depression. The study found that from 1929 to 1932, yearly emissions of carbon dioxide were reduced by around 26%, and it was 1937 before the emissions returned to pre-1929 levels. The post-war boom, the scientists say, appears one of the key contributing factors toward the rapid global temperature rise prior to the late 1990s slow-down.
The paper also notes that local level practices can have a small effect too, such as relatively recent changes to rice farming in Asia that have cut methane production.
Why does this matter? Well, it’s the fact that human intervention has helped to slow man-made global warming that is key here and why this is important in the continued war against climate change denial. As the study’s author’s write:
“Paradoxically, the recent decrease in warming, presented by global warming sceptics as proof that humankind cannot affect the climate system, is shown to have a direct human origin.”
It should be noted that independent researchers commenting on the study feel it’s unlikely this is the whole story. Nevertheless, they say these findings are significant:
“The impact of this change is small but not negligible: without the reduction in CFC emissions, temperatures today could have been almost 0.1C warmer than they actually are,” the BBC quotes Professor Myles Allen from Oxford University as saying.
Other theories have been offered as to what might also have contributed to the global temperature pause, including that a cooling in equatorial Pacific waters has helped retard temperatures — but that’s only a temporary pause and soon the Pacific waters will once again begin warming.
There’s one other big takeaway from this study, and it’s a little hard to swallow: global temperatures will start to rise again, and probably soon.
Alex Sen Gupta, of the Climate Change Research Centre at the University of New South Wales in Australia, writes in a commentary on the study that the Montreal Protocol’s positive impact on global warming is, unfortunately, not going to last. “In the end, the continuing rise in other greenhouse gases, particularly carbon dioxide, will keep temperatures marching upwards.”
As recently as September, the United Nations has reiterated that it is “95% certain” that climate change is predominantly caused by humans. At the same time, the UN highlighted that global temperature pauses appear short-lived and, regardless of the cause, should not deter us from taking action now.
What all this adds up to, then, is a clear message. It is possible for human action to slow global temperature rises but that it appears it will take a coordinated global effort far exceeding the scope of the Montreal Protocol to do so, action that, as yet, no world power has been able to initiate.
Photo credit: Thinkstock.
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