Scientists Stumped to Explain 18 Year Pause in Global Warming 1

No Global Warming in 18 Years ChartFigure 1. The least-squares linear-regression trend on the RSS satellite monthly global mean surface temperature anomaly dataset shows no global warming for 18 years 2 months since October 1996. The hiatus period of 18 years 2 months, or 218 months, is the farthest back one can go in the RSS satellite temperature record and still show a sub-zero trend.

New Study:  “Uncertainty in the magnitude of aerosol-cloud radiative forcing over recent decades” (Download PDF)


Aerosols and their effect on the radiative properties of clouds are one of the largest sources of uncertainty in calculations of the Earth’s energy budget. Here the sensitivity of aerosol cloud-albedo effect forcing to 31 aerosol parameters is quantified. Sensitivities are compared over three periods; 1850-2008, 1978-2008 and 1998-2008. Despite declining global anthropogenic SO2 emissions during 1978-2008, a cancellation of regional positive and negative forcings leads to a near-zero global mean cloud-albedo effect forcing. In contrast to existing negative estimates, our results suggest that the aerosol cloud-albedo effect was likely positive (0.006 to 0.028 Wm-2) in the recent decade, making it harder to explain the temperature hiatus as a forced response. Proportional contributions to forcing variance from aerosol processes and natural and anthropogenic emissions are found to be period dependent. To better constrain forcing estimates, the processes that dominate uncertainty on the timescale of interest must be better understood.

One of the leading explanations of the decade-and-a-half “pause” in global warming is that aerosols – fine particles of various kinds, mostly man-made, but also volcanic in origin – have increased the albedo (reflectiveness) of clouds.  The cooling effect of high pollution in the early period of the industrial revolution in the 19th and early 20th century is well known and documented.

Geophysical Research Letters, one of the leading scientific journals in the climate world, has posted a pre-publication copy of a forthcoming paper that has gone through complete peer review casting significant doubt on this hypothesis. “Uncertainty in the magnitude of aerosol – cloud radiative forcing over recent decades” was conducted by ten scientists from the leading climate science establishments mostly in Brittain.

Translation: The findings of this study indicate that the “aerosol” explanation of the warming pause is not supported by data – and at least ten respected scientists are saying we don’t know enough about how this works.  Previous claims are that current albedo cloud effects are negative, and thus holding down warming by virtue of reflecting sunlight, while this new study suggests the current cloud albedo effect is slightly positive (that is, warming, though very slightly).

One argument previously held is that if China, India, and other countries follow the United States and Europe in reducing particulate pollution, the reflective effect of clouds will diminish and warming will resume.  But with this study that hypothesis needs to be rethought. (Source)

Note:  RSS research is supported by NASA, NOAA, and the NSF, with many of their researchers participating in NASA science research teams and working groups, collaborating with other fore-front industry leaders and the scientific community. (Source)


In 1999 the IPCC reported that aircraft contrails and thin, high Cirrus clouds tend to warm surface temperatures.

This new paper is also consistent with our observation that chemtrails are frequently captured on camera appearing less reflective than normal clouds – an observation consistent with the authors’ finding that cloud albedo was found to be positive (warming) rather than negative (cooling). – Hsaive

Jet Aircraft Release of Aerosols That Warm the Climate

The existence of the pause in global warming was acknowledged by the IPCC last year (2013) but there has been significant debate about the actual duration of this hiatus with some commentators alleging that the length is exaggerated by cherry-picking the start date as 1998 – a particularly warm year.

McKitrick says that the statistical analysis technique he used avoids potential biases and is immune to the charge of cherry-picking.

“…we compute a hiatus length of 19 years, and in the lower tropospheric data we compute a hiatus length of 16 years in the UAH series and 26 years in the RSS series”. –

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