Dr. James Hansen, Makiko Sato and Reto Ruedy have completed their analysis of the 2013 global temperature through the Goddard Institute for Space Studies data set.
Statement from the report.......
The recent slowdown of global warming is a consequence of both a slowdown in the growth rate of climate forcings and recent ENSO history. Given that the tropical Pacific seems to be moving toward the next El Niño, record global temperature is likely in the near term. However, the rate of future warming will depend upon changes of the tropospheric aerosol forcing, which is highly uncertain and unmeasured.
Key points from the report.........
--Rate of global warming was slower in the past decade than the prior three decades.
--Likely reasons for the reduced rate of warming are slower growth of net climate forcings and cooling in the tropical Pacific Ocean.
--Continued trend of increasing frequency of extreme hot summer anomalies over land continued despite Pacific cooling.
--There is a substantial likelihood of an El Nino beginning in 2014, which would probably result in a record high global temperature for 2015.
--The 14 warmest years in the GISS record going back to 1880 have all occurred since and including 1998.
--Weakening of a weak La Nina like cooling of the equatorial eastern Pacific during the Fall helped contribute to 2013 having the 2nd warmest Sep-Nov in the 134-year record.
--Leveling off of global temperatures from 1940-1975 is generally attributed to an approximate balance of aerosol cooling and greenhouse gas warming during a period of rapid growth of fossil fuel use with little air pollution control. However, this not a given due to the lack of actual aerosol measurements.
--Despite the first 3-years of the present decade averaging about the same in terms of temperature compared to the previous decade, we have high confidence that the present decade as a whole will still end up warmer than the previous decade due to the fact that the planet is out of energy balance. That is, more energy coming in compared to going out. This is mainly due to increasing greenhouse gases over century, which are expected to further increase.
--Large volcanic eruptions are always a wildcard and can lead to significant, short-term cooling.
Key excerpts from the report.....
In contrast, winter temperature over land has declined in the past 10 years. There has been recent speculation that observed loss of Arctic sea ice may spur winter cold air outbreaks. On the other hand, Fig. 6a shows that there have been large oscillations in winter land temperature in the past when large Arctic sea ice reductions are not known to have occurred and seem unlikely, although accurate sea ice data are not available for those earlier times. Kosaka and Xie simulations suggest that the recent winter cooling is more a consequence of tropical ocean temperatures. Climate models yield larger long-term warming in winter than in summer, even when considering only land areas. Thus the recent downturn of winter temperature over Northern Hemisphere land is unlikely to continue.
We conclude that solar forcing is not negligible and contributed modestly to the global warming slowdown in the past decade, but its effect was small 16 and overwhelmed by long-term growth of GHGs, as confirmed by the fact that Earth was out of energy balance, more energy coming in than going out, even during the deep 2005-2010 solar minimum.
We conclude that a slowdown of the growth rate of the net climate forcing probably contributed to the slowdown of global warming in the past 15 years. The slower increase of climate forcing cannot by itself account for a long global temperature standstill, because we know that the planet continued to be well out of energy balance, more energy coming in from the sun than energy radiated to space. The dynamic variability of tropical Pacific sea surface temperature, i.e., the ENSO (El Nino Southern Oscillation), 2 can play a significant role on temperature change over a decade and it has a dominant role in interannual fluctuations.
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