Though the wildfires that have been ravaging Greece this summer finally seem to be under control, the damage done is enormous. More than a week of relentless blazes charred over half a million acres of farmland and villages, many people died and many more were injured. The government estimates the financial losses at more than $1.6 billion, a significant blow to the country’s relatively small economy.
Despite abundant warning about the coming conflagration, the government did nothing to prepare for it and much too little once it was underway. As one sign of warning, the country was battered by a series of unprecedented heat waves with temperatures persistently in the 100s, this following an exceptionally dry winter. Fires in other parts of Europe suggested what was to come.
More important in the long run, there’s empirical evidence that the incidence of wildfires is increasing in many parts of the world, and there’s strong theoretical evidence that this trend is going to continue. The Day Fire that raged in California last year was typical of the large wildfires that are predicted to plague many regions. That fire started on Labor Day, 2006 – hence the name — and burned for a month before firefighters finally controlled it. During that time it consumed more than 160,000 acres, becoming one of the biggest wildfires in California history.
Driven by erratic winds, the fire changed course suddenly and frequently, threatening communities on one side of the sprawling Los Padres National Park for a few days, then retreating and taking a shot at the other side. These volatile changes in direction exhausted the thousands of firefighters battling the blaze. Amazingly the loss of buildings was relatively small and no lives were lost, thanks to the efforts of the fire crews. They were supported by an impressive, and extremely expensive, array of engines, bulldozers, helicopters, and air tankers.
As the Earth warms a growing number of researchers are investigating, logically enough, the far-reaching consequences of the increasing average temperature. One of these consequences that is beginning to stand out is the effect on wildfires.
Because record-keeping there is so complete, scientists have studied the entire western United States and Canada in great detail. Snowpacks are critical to keeping the fire danger low in these areas until spring melt ends. And the snowpack has been changing dramatically. Since 1950, the winter snowpack, the source of 75% of the West’s water, has declined by up to a third in the northern Rocky Mountains region and by more than 50% in parts of Canada. In fact, the West is experiencing a prolonged drought that may be the worst since record-keeping began more than a century ago.
Once snowmelt is complete a forest can quickly become combustible because of low humidity and sparse summer rainfall. Over the 34 years covered by one study, those years with early snowmelt and hence a longer dry summer had five times as many wildfires as years with late snowmelt.
Snowpacks are now melting 1 to 4 weeks earlier than they did 50 years ago, and the wildfire data reflect this change. For example, since 1986 longer, warmer summers have resulted in a fourfold increase of major wildfires in the western US and a sixfold increase in the area of forest burned, compared to the period from 1970 to 1986. A similar increase in wildfire activity occurred in Canada from 1920 to 1999. Put somewhat differently, the length of the active wildfire season in the western US has increased by 78 days, and the average duration of large fires has increased from 7.5 to 37.1 days.
The fires in Yellowstone Park in 1988 seemed to inaugurate the new era of major wildfires. They lasted a total of more than 3 months, burning 600,000 hectares of forest. Despite the deployment of 25,000 firefighters and expenditure of $120 million, the fires weren’t extinguished until snow began to fall in mid-September.
The Yellowstone fires exhibited some of the common statistics of wildfires: Less than 5% account for more than 95% of the area burned. A small fraction of them get very large and become uncontrollable despite human efforts and expenditures of large amounts of money to suppress them.
The Fourth Assessment of the Intergovernmental Panel on Climate Change (IPCC), released earlier this year, gave some indications of what to expect in the future. Investigators ran several general circulation models to predict future climate conditions for several different possible emissions of carbon. The models unanimously predict June to August temperature increases of 2 to 5 degrees Celsius by 2040 to 2069 for western North America, and decreases in precipitation of up to 15% during that period. Applying these projections conservatively suggests that wildfire burn areas in Canada will increase by 74% to 118% in the next century, with a similar increase in the western US.
Studies by the world’s leading climate scientists leave no doubt that the future will certainly bring increases in average temperature, and perhaps less rain in some critical regions. The trend toward more wildfires, burning for longer durations, will continue.
But there’s another, potentially much more dangerous problem. An important aspect of any large-scale physical process is the influence of that change on further change. This is called feedback. It’s positive if the original change stimulates further change in the same direction, negative if the stimulated change is opposite to the original.
Wildfires, like other common combustion, release the major greenhouse gas carbon dioxide. Alarmingly, the amount released is substantial; one estimate puts the total amount released at about 40% of emissions from combustion of fossil fuel. Increases in wildfire activity, produced by global warming due to increasing greenhouse gas concentrations in the atmosphere, promotes putting more greenhouse gas in the atmosphere: positive feedback. In short, as global warming increases the frequency and duration of wildfires, these new sources of greenhouse gases in turn accelerate global warming.
Accounts in the media of recent reports released by the IPCC have focused chiefly on only a few of the threats from global warming. Rising sea level, increases in severe disease, extended drought, and lack of water because of the disappearance of glaciers are among the most common. Increasing wildfire activity has received little attention.
But the cost of these fires is considerable, both because of the property damaged or destroyed and the enormous expense required to fight them, often ineffectively. Perhaps most significantly, a major consequence of wildfires is the large contribution they make to the greenhouse gases in the atmosphere, and so to further global warming.