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Don Paul: If wildfires seem more common, there's a reason for that

Wildfires, droughts and heat waves existed long before climate change and warming accelerated. There were numerous periods in which such fires, sometimes calamitous, became more widespread.

Since there is no doubt mean global warming is occurring and accelerating, does that mean these disasters are becoming so much more common they deserve the descriptor “new normal”?

After perusing some of the literature, I would say whether this is the new normal isn't settled, but the evidence continues to point in that direction. This graphic from Wildfire Today, a journal that tabulates wildfire impacts, shows that the size of wildfires has been increasing as warming and drying has accelerated.

Here's a look at wildfires so far this year in California:

And take a look at how many have broken out across at least 14 states.

The amount of total acreage affected by wildfires, larger and smaller, has also been increasing.

However, Wildfire Today also points to a number of factors that may be important in determining why the size of fires has been increasing, in addition to climate change:

  • Warmer and drier weather makes fires harder to suppress.
  • A century of fire suppression has led to forests that are more dense and fires that burn with greater intensity.
  • For safety reasons, less-aggressive strategies are being used on large fires more often.
  • More fires are allowed to burn naturally for environmental concerns.
  • We may be initially responding to the new fires with less equipment and personnel.
  • The gradual 30 to 70 percent reduction in the number of large air tankers on exclusive-use contracts until 2014, when restoration of the fleet began.

In general, warming contributes to causing more heavy precipitation events in wet regions of the globe and more drought in arid and semi-arid regions. In the latter, warming temperatures increase the rates of evaporation from soil and plant life.

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One peer-reviewed study shows the extent of very dry regions globally has about doubled since the 1970s. Other studies come up a little short of that doubling, but show similar trends. (In wetter regions, the warming leads to more upward motion in the moist atmosphere, producing more precipitation.) Dozens of climate models projected these trends, which are already evident and appear to be increasing in the global mean. Warming also hastens the onset of snow melt, which expands the dry season in places like the American West.

An example of the impact from the lengthened dry season in California became evident last year. After a five-year severe drought, California finally had a wet winter. Lush vegetation bloomed where nothing had been growing for years. When last year’s normal dry season hit, that vegetation dried and became a vast storehouse of fuel for wildfires. Obviously, the same processes are occurring again right now. What we are seeing in places like California are longer, more frequent droughts which, when finally broken, lead to an explosion of vegetation during spring providing more fire fuel in the normally dry summertime.

It’s a vicious feedback, and the overwhelming evidence is we’re making it worse through the continued burning of fossil fuels.

Most climate scientists, such as Michael Mann of Penn State, still believe we can make a difference by reducing the use of fossil fuels and developing more energy-efficient methods of raising livestock and growing our crops. In other words, there are many experts who are not yet convinced we have reached a “tipping point” from which there may be no return. In their view, there is hope, based on reasonable science, economics and good planning, combined with a will to adjust our technology and energy generation.

However, a far more pessimistic note has been struck this week in a newly released study from the prestigious Proceedings of the National Academy of Sciences. “Trajectories of the Earth System in the Anthropocene.” It’s a heavy read, but the abstract is digestible enough:

We explore the risk that self-reinforcing feedbacks could push the Earth System toward a planetary threshold that, if crossed, could prevent stabilization of the climate at intermediate temperature rises and cause continued warming on a 'Hothouse Earth' pathway even as human emissions are reduced. Crossing the threshold would lead to a much higher global average temperature than any interglacial in the past 1.2 million years and to sea levels significantly higher than at any time in the Holocene. We examine the evidence that such a threshold might exist and where it might be. If the threshold is crossed, the resulting trajectory would likely cause serious disruptions to ecosystems, society, and economies. Collective human action is required to steer the Earth System away from a potential threshold and stabilize it in a habitable interglacial-like state. Such action entails stewardship of the entire Earth System — biosphere, climate and societies — and could include decarbonization of the global economy, enhancement of biosphere carbon sinks, behavioral changes, technological innovations, new governance arrangements and transformed social values.

In their conclusion, the authors readily admit much more research needs to be done. “Our initial analysis here needs to be underpinned by more in-depth, quantitative Earth System analysis and modeling studies to address three critical questions. (i) Is humanity at risk for pushing the system across a planetary threshold and irreversibly down a Hothouse Earth pathway? (ii) What other pathways might be possible in the complex stability landscape of the Earth System, and what risks might they entail? (iii) What planetary stewardship strategies are required to maintain the Earth System in a manageable Stabilized Earth state?”

Other than the journal editorial process, peer review has yet to begin. Whether or not this study is overstating the case, there is simply no denying the rate of mean global warming is accelerating. This is from exhaustively reviewed global data, supplied via NASA:

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