Study: Hottest Decade on Record Would Have Been Even Hotter But for Chinese Coal Plant Sulfur Pollution

Research reveals decade of global warming from China’s coal power stations has partly been offset by ‘cooling’ effect of sulphur pollution

That’s the UK Guardian headline for a half-clever new study, “Reconciling anthropogenic climate change with observed temperature 1998–2008.”

Last decade was easily the hottest on record, as were the 1990s and, before that, the 1980s — all part of a multi-decadal trend driven primarily by human-caused emissions.

We’ve known for a while that warming appeared to slow over a short, cherry-picked time frame of 1998 to 2008 because:

  1. The starting year (1998) was a very strong El Niño, which temporarily boosts global temps, and the ending point (2008) was a moderate La Niña, which lowers them.
  2. The end point was near the bottom of “the deepest solar minimum in nearly a century.”
  3. One key global temperature dataset, the Hadley/CRU one used by the UK’s Met Office, had numerous flaws that led to a slower warming trend than most of the others.

Even so, as we’ll see the land and the oceans just kept warming. It is just hard to stop the radiative forcing of the CO2 humans have put in the air, which equals 1 million Hiroshima bombs a day.

What’s clever about the new Proceedings of the National Academy of Sciences study is it demonstrates that sulfur pollution from China’s massive buildup of coal plants also helped slow the warming:


The finding that the recent hiatus in warming is driven largely by natural factors does not contradict the hypothesis: “most of the observed increase in global average temperature since the mid 20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations (14).” As indicated in Fig. 1, anthropogenic activities that warm and cool the planet largely cancel after 1998, which allows natural variables to play a more significant role. The 1998–2008 hiatus is not the first period in the instrumental temperature record when the effects of anthropogenic changes in greenhouse gases and sulfur emissions on radiative forcing largely cancel. In-sample simulations indicate that temperature does not rise between the 1940’s and 1970’s because the cooling effects of sulfur emissions rise slightly faster than the warming effect of greenhouse gases. The post 1970 period of warming, which constitutes a significant portion of the increase in global surface temperature since the mid 20th century, is driven by efforts to reduce air pollution in general and acid deposition in particular, which cause sulfur emissions to decline while the concentration of greenhouse gases continues to rise.

The results of this analysis indicate that observed temperature after 1998 is consistent with the current understanding of the relationship among global surface temperature, internal variability, and radiative forcing, which includes anthropogenic factors that have well known warming and cooling effects.

What’s not clever about this study is that it repeats the myth that there was a ‘hiatus’ in the first place. The top figure, from John Cook’s Skeptical Science website, makes that clear.

And that’s without even discussing the oceans, where climate science says the vast majority of the warming goes:

There has been no hiatus in global warming.

I have no clue why the PNAS authors use the favorite cherry-picked endpoints of the deniers, designed to minimize the actual trend. Or why they seem unaware that in the NASA dataset 2005 was the warmest year on record — and that 2010 was tied for the warmest year, according to NASA, NOAA, and the World Meteorological Organization.

They seem unaware of the June 2010 analysis by NASA that found:

“We conclude that global temperature continued to rise rapidly in the past decade” and “there has been no reduction in the global warming trend of 0.15–0.20°C/decade that began in the late 1970s.”

The Met Office has been ignoring the warming in the places where it has been warming the most–especially the Arctic — which they themselves acknowledged in a 2009 analysis (see Finally, the truth about the Hadley/CRU data):

… in data-sparse regions such as Russia, Africa and Canada, warming over land is more extreme than in regions sampled by HadCRUT. If we take this into account, the last decade shows a global-mean trend of 0.1 °C to 0.2 °C per decade. We therefore infer with high confidence that the HadCRUT record is at the lower end of likely warming.

That was published 18 months before the PNAS paper!

Indeed, in November 2010, the Met Office Hadley Center admitted they had flawed data — that led them to underestimate the rate of recent global warming. The Guardian itself reported at the time:

World is warming quicker than thought in past decade, says Met Office

… Including the new sea surface temperatures, which push up global temperatures by 0.03C, the warming rate for the past 10 years is estimated at 0.08–0.16C.

So it is odd that the Guardian gets this wrong now.

But the key point is that it now seems clear that when you accurately model all of the data and all of the forcings, the surface temperature data shows, as NASA said last year, “global temperature continued to rise rapidly in the past decade” and “there has been no reduction in the global warming trend of 0.15–0.20°C/decade that began in the late 1970s.”


The know-nothing anti-science deniers are touting the not-clever part of the study to brag that a peer-reviewed paper vindicates their inane, cherry-picked talking point that ‘there wasn’t warming from 1998 to 2008.’ This is doubly bizarrely.

First, even this study makes clear that there was warming consistent with our current understanding of climate science and forcings — it was just masked:

Declining solar insolation as part of a normal eleven-year cycle, and a cyclical change from an El Nino to a La Nina dominate our measure of anthropogenic effects because rapid growth in short-lived sulfur emissions partially offsets rising greenhouse gas concentrations. As such, we find that recent global temperature records are consistent with the existing understanding of the relationship among global surface temperature, internal variability, and radiative forcing, which includes anthropogenic factors with well known warming and cooling effects.

[Note to the authors, the last 11-year solar cycle was not “normal.”]

Second, as the lead author explains:

But rather than suggesting that cutting carbon emissions is less urgent due to the masking effect of the sulphur, Prof Robert Kaufman, at Boston University and who led the study, said: “If anything the paper suggests that reductions in carbon emissions will be more important as China installs scrubbers [on its coal-fired power stations], which reduce sulphur emissions. This, and solar insolation increasing as part of the normal solar cycle, [will mean] temperature is likely to increase faster.”

The time to start ignoring the dangerous falsehoods of the climate science deniers was a long time ago, but now is better than later — at least if we want a fighting chance to preserve the health and well-being of billions of people, including our own children and grandchildren.