University of Oxford researchers have confirmation: we're causing climate change, natural factors have very little to do with it.
Human activity and other external factors are responsible for climate warming, the paper reports. This, in itself, isn't exactly news; there has been consensus around the issue in the scientific community for a long time now. One piece of the puzzle, however, remained unclear -- what effect natural ocean currents had on climate patterns over the course of multiple decades. This lack of understanding has been leveraged by some to throw the whole thing into question.
The new paper, however, is clear: natural ocean-cycles have very little to no effect on global warming.
Man-made climate change
"We can now say with confidence that human factors like greenhouse gas emissions and particulate pollution, along with year-to-year changes brought on by natural phenomenon like volcanic eruptions or the El Niño, are sufficient to explain virtually all of the long-term changes in temperature," says study lead author Dr Karsten Haustein.
"The idea that oceans could have been driving the climate in a colder or warmer direction for multiple decades in the past, and therefore will do so in the future, is unlikely to be correct."
For the study, the team of researchers at the Environmental Change Institute looked at ocean and land surface temperature measurements since 1850. Apart from human-induced factors such as greenhouse gas concentrations, the analysis also looked at other occurrences such as volcanic eruptions, solar activity, and air pollution (both natural and anthropic).
The key finding that the authors report on is that slow-acting ocean cycles don't explain changes in global temperatures, including several decades of accelerated or slowed warming. The paper shows that the 'early warming' period (1915 -- 1945) was also caused by external factors. Formerly, this period of warming had been largely attributed to natural ocean temperature changes, which fueled uncertainty around the effect of unpredictable natural factors on climate.
"Our study showed that there are no hidden drivers of global mean temperature," says co-author Dr Friederike Otto. "The temperature change we observe is due to the drivers we know."
"This sounds boring, but sometimes boring results are really important. In this case, it means we will not see any surprises when these drivers -- such as gas emissions -- change. In good news, this means when greenhouse gas concentrations go down, temperatures will do so as predicted; the bad news is there is nothing that saves us from temperatures going up as forecasted if we fail to drastically cut greenhouse gas emissions."
The paper "A limited role for unforced internal variability in 20th century warming" has been published in the Journal of Climate.
