Burning the Carbon Sink

by Lindsay Wilson



My home is burning at the moment.  Not the bricks and mortar I live in here in the UK, but the place I call home. The coastal region of New South Wales. In fact there is a 750 ha fire about 20km from my parents’ house as I write this.

Bush fires are part of life in Australia, and they always have been.  But the fires at the moment are very early in the season, so people back home are asking if the fires are related to climate change.

Linking a single fire with climate change isn’t very sensible, particularly while peoples’ homes are still burning.  But the long term link between climate change and the risk of heat related extreme weather events, like fire and heatwaves, is gradually being understood.  It is a link which is better evidenced than for things like hurricanes and floods, where robust trends are virtually non-existent.

According to the CSIRO ”Australian annual average daily mean temperatures have increased by 0.9°C since 1910″.  In January it was so hot the Australian Bureau of Meteorology added some new colors to the legend on its heat map (above), the purple indicating above 50°C (122°F).  As we have hotter and longer summers we face increased risks of heat related dangers, one of which is fires.

The current fires and the bit of climate debate they have provoked has gotten pretty ugly back home.  But the vivid images serve to remind me of something else that I never read in the papers; the vulnerability of the carbon cycle to the risk of fire, and other feedbacks, in the coming century.



In my recent climate science for beginners post I talked about why scientists are uncertain as to how much the planet will warm by the end of this century.  The two reasons that are often discussed are the path of future emissions and climate sensitivity.  But there is also a third important factor.  The future of carbon sinks.

If it wasn’t for the increased absorption of carbon dioxide by the oceans and land sinks since the industrial revolution atmospheric concentrations of CO2 would already be above 500 ppm, and the world would be much warmer.



Of the total carbon dioxide emitted by human activity since 1750 about 44% remains in the atmosphere, 30% has been absorbed by the ocean and 26% by land sinks including trees, soils and fungi.

I’ve shown the annual sources of carbon emissions before, but where those emissions go in terms of sinks is hugely important too.



As humans emit more and more carbon dioxide each year the atmospheric concentration of CO2 increases, while both land and ocean sinks also absorb more CO2.  While absorption from the ocean has grown steadily, there is large annual variability and uncertainty surrounding land sinks.

If recent land sink growth is the result of CO2 fertilization and nitrogen deposition then land sinks may continue to absorb more and more carbon.  Whereas if they are largely a response to past land use change in terms of regrowth and thickening they may weaken, exacerbating warming.

Such uncertainties seem common when looking at carbon sinks.  Higher temperatures are generally associated with lower net absorption but increased CO2 and rainfall with more.  Fire are an issue too.

During the 20th century annual carbon emissions from fire increased by around 40%, driven largely by increased tropical forest fires (see Mouillot).  Some fires like the Amazonian fires of 1997/98 and the Black Dragon fires in China and Siberia in 1987 were big enough to have a discernible impact on global atmospheric concentrations.



If it wasn’t for the land and ocean sinks carbon dioxide concentrations would be growing at 4.8 ppm each year, rather than the recent average of 2.0 ppm. If you priced this mitigation service at $25/t CO2, it would be worth half a trillion dollars each year. But if you like the ocean, the price being paid in terms of acidification is virtually incalculable.

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Some good points. I've often said that eventually our carbon sinks would turn into net carbon emitters.

Just like bush fires are a part of living in Australia, so too climate change is a part of the natural cycle of the Earth.

Natural disasters are not new or out of the norm, they have always occurred and continue to do so.

Until it can be proven that man's tiny amount of CO2 emissions are causing the earth to heat up, you cannot blame climate change.

And even then you have to remember we are coming out of a mini ice age.

Its only natural that temperatures go up and CO2 rises.

Who knows what's normal.....????

Has Earth's climate ever been normal....????

What is normal....................??????

# wrote on Oct 28^th, 2013 at 7:33pm:


It would have to be an attempt much better than the pseudo science of the IPCC which has struggled to prove anything of significance.

And yet governments around the world are opening their cheque books.

Ajax wrote on Oct 26^th, 2013 at 4:23pm:


What was normal for the Cambrian period is not normal today.  "Normal" doesn't mean much in this context. There is a global population of about 7 billion, and resources are stretched. A rapid rise in temperature such as we'll experience over the next 100 years at least will reduce yields of staple food crops. In the medium term in some regions, there will be a net increase in productivity, but it's not sustainable as temperatures rise beyond around 2 degrees compared to the 1990 reference point. This is known from agricultural research, including some from staunchly conservatve researchers.

Is it normal to have massive declines in population due to food shortages? There have been mass extinctions in the past. Maybe it is, but is it desirable?

If you were to drop down dead from lung cancer, that would be quite normal too. People die from lung cancer all the time. It's normal for our population - but is it desirable?