A report released this month by the World Bank bears some upsetting news: without a redoubled commitment to reduce global greenhouse gas emissions, the world will very likely warm by an average of 3-4° Celsius by the end of this century. (That's 5.5-7°Fahrenheit.) For parts of the California desert that already regularly experience long stretches of daytime temperatures exceeding 100°, considering a boost of seven more degrees Fahrenheit is daunting indeed. But what would a 4°C increase in global temperatures really mean for the California desert?
The World Bank report, Turn Down The Heat: Why a 4 degree centrigrade warmer world must be avoided, prepared by the Potsdam Institute for Climate Impact Research and Climate Analytics, states that while we could still limit global average temperature increase to 2°C, current policies and emissions targets will likely result in at least a 3-4° increase by the end of the century. From the report:
The emission pledges made at the climate conventions in Copenhagen and Cancun, if fully met, place the world on a trajectory for a global mean warming of well over 3°C. Even if these pledges are fully implemented there is still about a 20 percent chance of exceeding 4°C in 2100. If these pledges are not met then there is a much higher likelihood--more than 40 percent--of warming exceeding 4°C by 2100, and a 10 percent possibility of this occurring already by the 2070s, assuming emissions follow the medium business-as-usual reference pathway. On a higher fossil fuel intensive business-as-usual pathway... warming exceeds 4°C earlier in the 21st century. It is important to note, however, that such a level of warming can still be avoided. There are technically and economically feasible emission pathways that could still limit warming to 2°C or below in the 21st century.
A 4° increase is approximately the same degree of difference as between our pre-industrial climate and the height of the last Ice Age, but while temperatures warmed from Ice Age levels over a period of thousands of years, this rise will come within a human lifetime, giving the planet's ecosystems precious little time to adapt.
That's a 4° average increase. Some parts of the world will see greater increases than that. The report projects increases of as much as 6°C -- almost 11° Fahrenheit -- in the Mediterranean, North Africa, the Middle East, and the contiguous United States. We saw a foreshadowing of that future this past summer, as temperatures in the Plains states rose to as much as 12°C higher than usual in the third week in June.
Though the correlation isn't exact, increased temperatures are often accompanies by increased aridity, and this past summer provides yet another example in North America. Throughout the summer months, a record drought took hold over the majority of the Western and midwestern United States, in some regions to a degree unparalleled since the 1880s.
As you can see, though the worst of the drought centered on places well to the east of California, the California desert suffered severe, long-term drought this past summer -- with neighboring desert areas in northern Nevada tipping over into extreme drought conditions.
Long-term drought is of special concern for ecological modeling: while a short-term drought may cause serious damage to agriculture and some annual wild plants, a longer drought means die-off of desert trees, mature shrubs, and other organisms that have the reserves to weather a short period of aridity. That's part of what ecologists refer to when they talk about things like the eventual die-off of Joshua trees from within Joshua Tree National Park: drought causes stress not only on the trees, but also on animals in the vicinity that may turn to eating the trees' vascular tissue in order to get a little water, killing the trees. Many desert organisms can withstand higher temperatures than they usually see so long as they have sufficient water. Raise the temperatures and impose a drought and organisms from junipers to jackrabbits will suffer.
Drought also means less runoff in the Colorado River basin, in turn meaning less water in the river. The Colorado is already oversubscribed -- there are more claims on the water than there is water. Drying up the river even more means some current water users will have to go without. In all likelihood, that means less water going to agriculture, and irrigated desert farms across the Southwest going fallow. Without either healthy crops or native vegetation to hold the soil in place, that soil is going to go airborne every time the wind picks up -- and a warmer world means more frequent and more powerful storms. The haboobs that have swept out of Arizona and into California over the last couple of years will very likely become a far more frequent occurrence.
As for overall environmental impacts, the World Bank report projects serious disruption to biodiversity even at a 2.5°C increase, with a 4° increase nearly inevitably bringing about sharp ecosystem disruptions:
In a scenario of 2.5°C warming, severe ecosystem change, based on absolute and relative changes in carbon and water fluxes and stores, cannot be ruled out on any continent. If warming is limited to less than 2°C, with constant or slightly declining precipitation, small biome shifts are projected, and then only in temperate and tropical regions. Considerable change is projected for cold and tropical climates already at 3°C of warming. At greater than 4°C of warming, biomes in temperate zones will also be substantially affected. These changes would impact not only the human and animal communities that directly rely on the ecosystems, but would also exact a cost (economic and otherwise) on society as a whole, ranging from extensive loss of biodiversity and diminished land cover, through to loss of ecosystems services such as fisheries and forestry.
How will such a temperature increase affect desert people? Summers in the low desert already reach temperatures that would prove fatal to vulnerable people in the absence of air conditioning. Average high temperatures in Palm Springs, Indio and Mecca brush up against the 110°F mark, which means that it's hotter than that as much as half the time. Increases in temperature in the 4°C range (7.2°F) would push the Coachella and Imperial valleys' climate into the range currently enjoyed by Furnace Creek in Death Valley. A wide swath of California from Desert Hot Springs to Calexico would become essentially uninhabitable for people without sufficient wealth to pay high electric bills. So would Phoenix, with Tucson and Las Vegas not far behind. Barstow, the Morongo Basin, and the Antelope Valley would experience a climate similar to that of present-day Coachella.
That's not just going to make us feel somewhat uncomfortable on the walk between the air conditioned car and the air conditioned shopping mall. There are huge public health impacts of a warming world, many of which will be keenly felt by the desert's most vulnerable people. The 2003 heat wave in Europe pushed temperatures to 103°F or so, a range experienced by the Coachella Valley every summer, but as few people had access to air conditioning, 50,000 people are estimated to have died from heat exposure. Imagine if those temperatures had been ten or fifteen degrees higher. We can expect more and more heat waves that claim lives among the desert's homeless, indigent or disabled populations, especially if power blackouts increase. Higher temperatures will mean worse public health impacts from air pollution, including not just drought-aggravated particulate matter but smog-forming chemicals, whose toxicity will be heightened the hotter the temperature at which they're cooked.
That's just a quick overview of what the California desert faces if we don't get our greenhouse gas emissions under control.
Chris Clarke is an environmental writer of two decades standing. Director of Desert Biodiversity, he writes from Joshua Tree regularly at his acclaimed blog Coyote Crossing and comments on desert issues on KCET weekly. Read his recent posts here.