Statistically, humanity is almost certainly responsible for global warming
The world is getting warmer, with 13out of the 15 warmest years on record occurring in the currentcentury. But just how sure are we that humanity's burning of oil andcoal is the key factor in the temperature increase? A new project,led by researchers at the Potsdam Institute for Climate ImpactResearch, has answered that very question, working to estimate the likelihood of those temperature trends occurringnaturally.
That likelihood has been estimated tobe incredible tiny in the past, as low as 1 in 650 million. Theproblem is that natural climate change – warming that would occurwithout the presence of mankind – tends to gradually rise and fallover periods of at least several years at a time. That gradualprocess makes it difficult to accurately separate the natural andhuman causes of warming, in turn making it tough to arrive at a trulyreliable estimate.
To improve our understanding, thePotsdam Institute team used temperature data ranging from 1880 to2014 to map the recorded fluctuations, while using computersimulations of the planet's climate to take the natural warmingfactor into account. Once all the numbers were crunched, the teamfound the likelihood of the trend occurring naturally to be between 1in 5,000 and 1 in 170,000.
While those numbers are significantlyhigher than some other estimates, the researchers believe that theodds are low enough to suggest that the observed temperatures areextremely unlikely to occur without the impact of humanity'sgreenhouse gas emissions. In fact, the stats suggest that the recordtemperatures are roughly 600 to 130,000 times more likely to haveoccurred as a result of human emissions than without them.
Furthermore, while the data used forthe analysis only runs up until 2014, the temperature readings for2015, which arrived after the work was complete, show it to be thewarmest year on record. Had that data been included in the study,then the numbers would have been more damning, with the chance ofhumanity's actions not being the cause shrinking even further.
"Natural climate variations justcan't explain the observed recent global heat records, but man-madeglobal warming can," said study co-author Stefan Rahmstorf,summarizing the findings. "It has led to unprecedented local heatwaves across the world – sadly resulting in loss of life andaggravating droughts and wildfires. The risk of heat extremes hasbeen multiplied due to our interference with the Earth system, as ouranalysis shows."
The researchers published the findingsof their study in the journal Scientific Reports.