From the ABC 7 Weather team

Is China's coal pollution helping slow down global warming?

July 8, 2011 - 11:00 PM
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A recent study suggests that China's sulfur emissions are helping keep a lid on global warming. How should scientists deal with such unexpected drivers of climate change?

Haze and sulfur aerosol pollution produced by China seems to be countering the warming effects of carbon-dioxide emissions. (NASA)

We are sweating through the middle of a hot summer once again. What better time to jump back into the climate debate?

A few years back, I wrote a series on the science of climate change and, yes, the third rail some meteorologists refer to as “global warming.” Well, a paper recently published in the Proceedings of the National Academy of Sciences really got the blogosphere fired up – pro and con but unfortunately not much in between – about the climate. In particular, people are arguing about the effect that China’s rapid urbanization and burning of fossil fuels is having on global temperature changes. (Abstract, full paper.)

I think there are several interesting points to be drawn from the study, performed by researchers from Boston University, Harvard and Finland's University of Turku:

1) China more than doubled its consumption/burning of coal from 2004 to 2007. (The last time China’s coal consumption doubled, it took 22 years.)

2) Sulfur aerosol emissions created by burning coal tend to have a net cooling effect on the atmosphere.

3) Before 2002, there was a net worldwide decrease in sulfur emissions, primarily because of clean-air acts and mitigation efforts in the U.S. and Europe.

4) The cooling effects of sulfur aerosols has essentially countered any global temperature rise caused by increased levels of carbon dioxide.

5) This balancing act between sulfur and carbon dioxide, along with the slight decrease in solar energy during the solar minimum and the cool La Nina, meant there was essentially no statistically meaningful change in the global temperature from 1999 to 2008.

Does this mean all the recent scientific observations about humanity’s role in our changing climate have been wrong? Of course not.

It does mean, though, that there sure still is uncertainty about how we are affecting the earth’s land, water and air systems. Does every scientist agree the increase in carbon-dioxide concentration in the air and the oceans is primarily due to the more than 30 billion tons of the gas churned out by about 7 billion people worldwide burning carbon fuels? Yes, and be sure to let me know of one real climate scientist who thinks the famous Keeling Curve is a “hoax.”

keeling curve

The Keeling Curve displays rising levels of CO2 in earth’s atmosphere in recent years.

Here’s another important graph of what is called the decadal-scale climate prediction, put together by the U.K.’s Met Office. As you can see from the black line showing the Earth’s average surface temperature, there has been little change (or even a bit of cooling) in the stretch from 1998 to 2010:

decadal scale climate prediction

What is also interesting about this study is that it relied upon a simulation (or that dreaded word, “model”) of the natural and human “drivers” of long-term climate. However, the research team ran the simulation for a decade and changed the starting point of the “model” as the real world changed. Look at the above graph and what happened with worldwide temperatures when Mt. Pinatubo erupted in 1991.

Mt. Pinatubo climate change

The second largest terrestrial volcanic eruption of the 20th century injected some 20 million tons of sulfur aerosols into the air, forming a thin umbrella over the earth. Look at the earth’s temperature cool from 1992 to 1994 by almost 2 degrees. There was no climate “model” predicting a volcanic eruption in 1991, so the “forecast” for the next decade starting in 1996 used a cooler starting point and the forecast to 2005 was accurate within the uncertainty.

So what happened with the last decadal made in 2005 or thereabouts? Hello, China. It’s no volcano, but surely few predicted that the rapid growth of the Chinese economy and energy production largely driven by the burning of coal would inject as much sulfur aerosols in the air as has happened.

What is next? The past does give us some hints of the future. Take a look at this image from the National Climatic Data Center (yes, I know it’s another bloody graph… bear with me):

ncdc graph

The red bars are the global average temperature, the vertical bracket lines give an indication of the confidence of the data and the blue line is the long-term temperature average. The recent trend is relatively flat – just like it was in the 50s and 60s. What was going on then? Remember the Clean Air Act of 1963? That piece of legislation imposed new standards that greatly reduced the particulate emissions of the U.S. (then the greatest emitter of carbon dioxide, although China has since taken over in that respect).

The science is settled then, right? Nope. Science is never really “settled”; quantum physics and Isaac Newton still don’t agree on much. But words such as climate “denier,” “alarmist” and much worse sure don’t help any of us better understand what we are learning and about what 99 percent of climate scientists agree upon. Given all that we don’t know, could thousands of climate scientists and researchers be wrong? Sure, it’s possible, and a Nobel Prize is waiting for the scientist who validates that humans are having zero effect on the earth and its climate. 

There are still many things we have yet to learn about earth's climate in a warming world. The role and type (low ocean to high tropical) of clouds is high on the list. Also, when you look at various news stories and especially blog posts, you should always ask: "What's the uncertainty? What is the error? What is the confidence level of the forecast?"

As for what this all means for politics and policy, I’ll defer to our commenters and to Roger Pielke Jr. and his latest book "The Climate Fix." As our former president George H. Bush reportedly once said, going there myself “wouldn’t be prudent.”

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