Monday, December 30, 2019

Forest fires destroy about 10% of the world's forests every decade

Australia is suffering horribly from an intense heatwave and bush fires.

Are these fires caused directly by global warming? No.

Are these heatwaves and fires made more frequent, more intense by global warming? Yes.

Like all climatic events, the fires and heatwaves are multi-factorial. The Indian Ocean Dipole  (an oscillation like the El Nino/La Nina phenomenon) is in a strong positive phase at present, creating a warm sea surface and extensive flooding in East Africa (unreported in our media) and drought in Indonesia and Australia.

Australia has of course always been subject to intense heatwaves, and a conservative tweeter reports on such an event in 1790, the implication being "This is just a natural cycle".

Only it is not just a natural cycle, because the temperature of the planet is rising inexorably, which means that heat waves must necessarily become more frequent.

The conservative also shows this figure:

Wow! The area of forest fires burned is decreasing while Earth temperature T is increasing.
So fires cannot be related to climate change can they?

Let's have a closer look. The burned area columns are from Spatial and temporal patterns of global burned area in response to anthropogenic and environmental factors: Reconstructing global fire history for the 20th and early 21st centuries by Yang et al 2014, a serious piece of work. They found the area being burned is indeed decreasing in the tropics and the extra-tropics, although there was no trend in the temperate forests. Human activity was responsible for the trends in the tropics, and climate variation relates to the variations in temperate fires, with more fires in warm years. Rising temperatures and increased drought is expected to increase wildfires in many regions.

Globally, in the 1900s, forest fires destroyed 5 million sq km of forest,
and in the 2000s, they only destroyed only 3.6 million sq km.

Forest cover in 2006 is estimated at 39  million sq km, so the area burned was about 9.2% of the total.

What was global forest cover in the 1900s? We have a figure for estimated deforestation here. About 10.5 million sq km of forest (tropical + temperate) have been lost since 1900. Therefore the area under forest globally in the 1900s was
39 + 10.5 = 49.5 million sq km.

In that decade, the area burned was 5 million sq km, so the area burned was 10% of the total.

The proportion of forest burned over the last century has been remarkably constant.

In recent decades we have many effective ways of forestry management - with techniques like creating firebreaks, cleaning up forest litter (that is, the sticks and leaves that gather and when dry, create a fire risk), and of course, our ability to drop water on forest fires from the sky and from fire engines on the ground, which was not an option 100 years ago. These have hopefully reduced the extent of damage caused by forest fires, but something has stopped the effort translating into a reduction in the proportion of forest burned. That something may be global warming, with increased temperatures and perturbed precipitation patterns.

The improved fire-control techniques that we now have are offset by the increased global temperatures, and the intent of global warming deniers to show that global warming is unrelated to forest fires is another of their failures.

We need to put far more effort into helping the Australians to contain their fires.
Generally, we need early warning of fires so that they can be identified and put out when they are starting (drones and balloons might be useful here) and we need to put more effort into creating firebreaks an clearing litter.  Controlled burning, when fires are set a short time before expected rain, is good because fire is part of the natural cycle.

Forestry management needs to be part of the Green New Deal

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