Human activity continues to warm the planet over the past 16 years
What the science says...
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Once natural influences, in particular the impact of El Niño and La Niña, are removed from the recent termperature record, there is no evidence of a significant change in the human contribution to climate change.
Update 21/02/2013: Troy Masters is doing some interesting analysis on the methods employed here and by Foster and Rahmstorf. On the basis of his results and my latest analysis I now think that the uncertainties presented here are significantly underestimated, and that the attribution of short term temperature trends is far from settled. There remains a lot of interesting work to be done on this subject.
Global temperatures are affected by both natural and human factors. The human influence is dominated by a slow but inexorable warming caused by greenhouse gas emissions. Natural factors include strong but short lived changes due to El Niño, La Niña and volcanoes.
In order to reliably measure the human influence on climate it is necessary either to use temperature data covering several decades, or to first remove the effect of the natural influences. Both approaches give the same result - human activity is warming the planet.
A media myth has emerged disputing this fact. The myth is based on the fact that temperatures have risen more slowly over the past 16 years than previously. However this period is too short to eliminate the effect of short term natural influences on temperature, and no other attempt has been made to eliminate their effect. Therefore the conclusion is invalid.
The ‘16years’ video demonstrates how the natural influences can be removed from the temperature record, and that the rate of warming due to human activity shows essentially no change.
In order to address the general audience the language in the video has necessarily been heavily simplified. Additional information is provided in the video description and in the advanced version of this rebuttal.
- The 16-year temperature trend provides no evidence to suggest that human-caused greenhouse warming has slowed.
- The 16-year temperature trend provides no evidence to suggest that the consensus understanding of human-caused climate change is incorrect.
- The temperature record over the past 35 years is consistent with climate change being driven by human greenhouse gas emissions.
- Given that human greenhouse gas emissions are increasing, and that the natural influences do not show a trend on longer timescales, we must expect increasing global warming in the future.
The results of this analysis are consistent with a statement by WMO Secretary-General Michel Jarraud:
"Naturally occurring climate variability due to phenomena such as El Niño and La Niña impact on temperatures and precipitation on a seasonal to annual scale. But they do not alter the underlying long-term trend of rising temperatures due to climate change as a result of human activities"
The rest of the climate system
Focusing on surface air temperatures also misses more than 90% of the overall warming of the planet (Figure 2).
Figure 2: Components of global warming for the period 1993 to 2003 calculated from IPCC AR4 220.127.116.11.
Nuccitelli et al. (2012) considered the warming of the oceans (both shallow and deep), land, atmosphere, and ice, and showed that global warming has not slowed in recent years (Figure 3).
Figure 3: Land, atmosphere, and ice heating (red), 0-700 meter OHC increase (light blue), 700-2,000 meter OHC increase (dark blue). From Nuccitelli et al. (2012).
- Foster and Rahmstorf (2011), Global temperature evolution 1979–2010 doi:10.1088/1748-9326/6/4/044022
- Rypdal (2012) Global temperature response to radiative forcing: Solar cycle versus volcanic eruptions doi:10.1029/2011JD017283
- Nuccitelli et al. (2012) Comment on Ocean heat content and Earth's radiation imbalance. II. Relation to climate shifts doi:10.1016/j.physleta.2012.10.010
Credits: Calculations and video: Kevin C. Voiceover: Daniel Bailey. Advice: The SkS team.
Last updated on 21 February 2013 by Kevin C. View Archives