OH, HERE WE GO AGAIN… ANOTHER BORING GLOBAL WARMING RANT SEEMS TO ME, THE ICE USED TO BE A LOT THICKER THIS TIME OF YEAR… YOU MEAN DESPITE THE MOUNTAIN.

OH, HERE WE GO AGAIN… ANOTHER BORING GLOBAL

WARMING RANT

SEEMS TO ME, THE ICE USED TO BE A LOT THICKER THIS TIME OF YEAR…

YOU MEAN DESPITE THE MOUNTAIN OF HARD EVIDENCE, YOU STILL DON’T

BELIEVE IT?

OH, PLEASE… CAN YOU POINT TO

ANYTHING THAT SHOWS IT’S AS

DANGEROUS TO ME AS THEY CRACK IT UP

TO BE?

Effects of global warming on humans

(interpreted broadly)

Wildfires have consumed increasing areas of western U.S. forests in recent years, and fire-fighting expenditures by federal land-management agencies now regularly exceed US$1 billion/year. Hundreds of homes are burned annually by wildfires, and damages to natural resources are sometimes extreme and irreversible.

Recent, very large wildfires (>100,000 ha) burning in western forests have garnered widespread public attention, and a recurrent perception of crisis has galvanized legislative and administrative action.

A few examples…

Oakland Hills Fire in October 1991 destroyed 2,550 single-family homes, and 37 apartment and condominium units, and was one of the most deadly fires in recent history, killing 25 people including one police officer and one firefighter. It caused an estimated $1.5 billion in direct damage and burned 1,600 acres.

In 2003 and again in 2007 there were enormous

wildfires near San Diego, each at the end of especially

dry years.

Princeton’s Michael Oppenheimer put it this way:

The weather we’ve seen… may or may not be due to the global warming trend, but it’s certainly a clear picture of what the future is going to look

like if we don’t act quickly to cut emissions of the greenhouse gases.

Were the brutal San Diego wildfires directly caused by global warming?

The next few slides are modified from an important paper that links wildfires to global warming:

Warming and Earlier Spring Increase Western U.S. Forest Wildfire Activity

A. L. Westerling, H. G. Hidalgo, D. R. Cayan, T. W. Swetnam

Science 313, 940-943 (2006).

Forest wildfire activity in the western US is widely thought to have increased in recent decades, yet

neither the extent of recent changes nor the degree to which climate may be driving regional changes in

wildfire has been systematically documented.

Much of the public and scientific discussion of changes in wildfire frequency has focused instead on

the effects of 19th- and 20th-century land-use history.

Which is most responsible for the recent increases?

Competing explanations: Land-use versus climate

Land-use

•Fire frequency reduced by livestock grazing and fire suppression methods in the 20th century

• Forest regrowth after extensive logging and absence of extensive fires increased the fuel load, making it harder to fight fires. Thus they are bigger and last longer.

Climatic explanations

•Increasing variability in moisture conditions (wet/dry oscillations promoting biomass growth, then burning),

•And/or a trend of increasing drought frequency,

•And/or warming temperatures

have led to increased wildfire activity

In some cases these may be complementary.

Increased forest wildfire activity.

The incidence of large wildfires (>400 ha) in

western forests increased in the

mid-1980s

Subsequently, wildfire frequency

was nearly four times the average of 1970 to 1986,

and the total area burned was more than six times its

previous level. Wildfire frequency

is strongly associated with

spring and summer

temperature.

The frequency of fires also

correlates with the timing of the spring snowmelt. Early melting is

related to temperature.

Overall, 56% of wildfires and 72% of area burned in wildfires occurred in early snowmelt years. Only 11% of wildfires and

4% of area burned occurred in late snowmelt years.

The length of the wildfire season

also increased in the 1980s, both

because of earlier ignition and later control of fires.

Regardless of past trends, virtually all climate-model projections indicate that warmer springs and summers

will occur over the region in coming decades. These trends will reinforce the tendency toward early spring snowmelt and longer fire seasons. This will accentuate

conditions favorable to the occurrence of large wildfires, amplifying the vulnerability the region has experienced

since the mid-1980s.

The Intergovernmental Panel on Climate Change's consensus range of 1.5° to 5.8°C projected global surface

temperature warming by the end of the 21st century is considerably larger than the recent warming of less than

0.9°C observed in spring and summer during recent decades over the western region.

Current estimates indicate that western U.S. forests are responsible for 20 to 40% of total U.S. carbon sequestration. If wildfire trends continue, much of this carbon will be released, suggesting that the forests of the western United States may

become a source of increased atmospheric carbon dioxide rather than a sink, even under a relatively modest temperature-

increase scenario.

This is a good example of positive feedback that accelerates global warming.

• increased temperature increases fires;

• fires release CO2;

• CO2 increases temperature.

Hence, the projected regional warming and consequent increase in wildfire activity in the western United States is likely to

magnify the threats to human communities and ecosystems, and substantially increase challenges in reducing greenhouse

gas emissions.

The interaction of increased temperatures, the mountain pine beetle, and both lodgepole and jack pine trees provides another

good example of positive feedback.

The adult mountain pine beetle (Dendroctonus ponderosae) is less than one centimeter long. Damaged trees

turn red.

By the end of 2006, the mountain pine beetle

(Dendroctonus ponderosae) had ravaged 130,000 square

kilometers of forest in western Canada.

Though not the first time an outbreak has occurred in the region, the latest is an order of magnitude larger than any

previous attack and brings the total area of forest

destroyed between 1997 and 2007 to 13 million hectares.

Beetle populations have exploded because a series of mild winters has allowed the larvae to survive from one year to the next. There is now concern that they will be able to cross the

Rocky Mountains and infest timber in the east.

Not only is this bad news for the affected trees, whose fate is sealed once the beetle takes hold; the infestation also packs an atmospheric

punch. According to a recent report (Kurz et al, (2008) Nature 452, 987-990) the assault on British Columbia's pine trees could cause the

region to release more carbon dioxide than it absorbs from the atmosphere over the coming decade.

With fewer healthy trees available to absorb the greenhouse gas and more trees decaying and dying, this will further contribute to the

warming that is facilitating the pest's territorial spread.

According to the new calculations, by 2020 the beetle outbreak alone will have released 270 megatonnes of carbon dioxide into the

atmosphere. That's exactly the amount of greenhouse gas emissions that Canada is committed to reducing by 2012 under the Kyoto

Protocol. And given that Canada is far from meeting that target, it may be even harder than once thought for the nation to offset its

emissions through forest management.

Stating the results another way, the predicted emissions are larger than the total CO2 absorbed by all of Canada's managed forest over

the last decade.

Extending the positive feedback cycle further, pines infested by the beetle are much more susceptible to wildfires. Because the fires can spread into adjacent

uninfested forest, they will cause even more CO2 release.

CO2 warming

dead trees beetles

decay

fire

live trees