15 October 2009

Climate Change and Bushfires

That climate change should have a noticeable impact bushfire activity seems obvious; large bushfires are largely a manifestation of both short-term weather and climate convolved with vegetation dynamics (i.e. fuel), itself a function of weather and climate. What is less obvious are the exact details of how this interaction will play out.

One obvious effect is on the weather and climate. In many fire prone regions, heat waves and drought are projected to become more intense and/or more frequent. These trends will obviously increase the fire weather danger, producing more days with 'extreme' fire weather conditions. More days implies more chances for fires to ignite, more chances for existing fires to spread out of control, more chances for a dramatic human impact.

Less obvious is the effect on the vegetation side of things. As the climate changes, will the same types of vegetation continue to grow in a given location? If the forest burns down, will it always grow back? What about other, less-quantified effects like CO2 fertilization?

Fire is an ecological force. The combination of fire frequency, vegetation and plant types along with the weather and climate describes the 'fire regime' of a location. What is clear is that the fire regime of places will change with the climate. This depends on the location and the exact details of the change that occurs. For example, one place may witness a change from forest to grassland, perhaps resulting in more frequent, lower intensity fires. In another case, forest persists in the face of more frequent or more severe droughts, resulting in high fuel loads and hotter, more dangerous fires. In both cases, the fire regime changes. This is what happens with climate change. Organisms that fail to adapt to the new regime die or move on, the previous character of the locale is gone forever...

There is evidence of these changes in fire regime around the world; most obvious to identify is unusual or increased fire activity. In the western USA, fire activity and cost to society has increased dramatically since the turn of the century. Athens, capital of Greece, has seen two major fires wildfires in two years. In many places around the world, there has been an apparent uptick in fire activity and consequences.

Australia is no exception. The 21st century has to this point seen several major bushfire disasters, particularly in the southeast portion of the continent. Most recent are the events of 7 Feb 2009, Black Saturday. The Canberra bushfires were in 2003, while Victoria also saw a fire of over a million ha that year (as well as another in 2006-7...). Are these events 'caused by' climate change?

The question is difficult to answer with certainty. Some would argue that the relative lack of prescribed burning or the general incompetence of fire management authorities are to blame. There is at least a grain of truth in those arguments, at least as far as the scale of the disasters. There is also an uncertain history of fire in Australia. Fire is undoubtedly a major part of the ecosystem; the local history and mythology is filled with anecdotal tales of bushfire. But nothing is definitive; the data necessary to quantify the problem are lacking.

A highly improbable event like Black Saturday cannot be definitive of a climate change influence. We know that days with similarly outrageous fire danger scores have occurred before, for example, Ash Wednesday in 1983 was close. How often they happen is uncertain; once every 30 years or so is probably not a bad guess. These type of events occurring more frequently, say once a decade would provide more certainty. But that certainty is 20 or more years away, a long time to wait...That said, there is a tendency in the last 30 years or so towards overall higher fire dangers in many locations in Australia, particularly the southeast.

Despite this lack of certainty, I strongly believe that anthropogenic climate change is a reality that needs to be acted upon. Despite quibbles about the vagaries of the mean global temperature tendencies, there are many other independent lines of evidence. Many changes are underfoot. Globally, animal species are on the move, Ice caps and glaciers are melting, droughts are intensifying and becoming more frequent in many locations. All of these have their roots in human activity, not just climate change but other environmental misuse as well.

We know that we are making major changes our physical environment; we are changing the chemistry, physics and biology of the system. The final outcome of the Great CO2 Enhancement Experiment (40% and rising...) is not yet known, but early signs suggest that the result is unlikely to be favourable for either our civilization or the ecosystem upon which we depend. True, our action today may very well be too late or otherwise ineffective, but inaction guarantees a more difficult life for future generations.

This post was written in support of Blog Action Day.

If you like this post, then go and read my (currently inactive) blog planet doom?. It has heaps of posts about climate change and other human effects on the world around us, There are multiple posts on wildfire and climate change available.

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