by Emil Morhardt
A glance at the graph above, from the University of East Anglia Climatic Research Unit (http://www.cru.uea.ac.uk/), shows that the last two time periods covered (encompassing 2015) are warmer than at any time since 1850. In the prior decade, however, there was much less upward trend, feeding speculation, particularly from climate-change deniers, that all of the warming we have seen since 1900 was largely unrelated to anthropogenic carbon dioxide emissions. There was also speculation from other scientists that the apparent slowdown in warming was statistically “in the noise” and that, in time, there would be a rebound and that the monotonic upward trend since the mid-1970s would soon resume, as it now seems to have. Time will tell, of course, but mainstream climate scientists Fyfe et al. (2016) have just made a new analysis of the early 2000s warming slowdown and pronounce it real and probably largely attributable to the early 2000s’ negative phase of the Interdecadal Pacific Oscillation (IPO) in which intensification of the trade winds lowered sea surface temperatures enough to offset the warming from the ongoing increases in atmospheric greenhouse gases.
The full story is more complicated, of course, and the Fyfe et al. paper does a nice job of discussing solar irradiance changes, sulphate aerosols from volcanic eruptions, and other complicating factors, but the recent increases in warming (which they do not treat except by brief mention and intentionally avoided because of the unknown effects of the large 2015-2016 El Niño event…Fyfe, personal communication) is in keeping with the rebound in global temperature increases which many of us have been expecting.
Fyfe, J.C., Meehl, G.A., England, M.H., Mann, M.E., Santer, B.D., Flato, G.M., Hawkins, E., Gillett, N.P., Xie, S.-P., Kosaka, Y., 2016. Making sense of the early-2000s warming slowdown. Nature Climate Change 6, 224-228.