New research, soon to be published in Geophysical Research Letters by Thomas Reichler of the University of Utah and Jian Lu of the US National Center for Atmospheric Research in Colorado indicates, that as climate models have projected, the tropics are expanding.
To determine this, the researchers measured changes in the height of the tropopause (the boundary area between the troposphere, the lowest level of the earth’s atmosphere and the stratosphere, the layer directly above it). The tropopause is higher in the tropics than at the poles because the warmer air of the tropics rises higher than does the colder air of the poles, given that the atmospheric pressure is the same in both regions.
The red line indicates the location of the tropopause. As you can see, the closer you get to the equator, the higher the tropopause is.
Using the tropopause as a yardstick (PDF) Lu and Reichler have examined the expansion of the tropics since 1958. Using the tropopause data in a computer model the researchers confirmed a gradual poleward shift of the tropics at the average rate of 70 km per decade.
Previous studies have shown that the width of the tropical belt has been increasing since at least the late 1970s based on a variety of metrics. One such metric, the frequency of occurrence of a high-altitude tropopause characteristic of the tropics, is used here to show that the observed widening of the tropics can be accurately replicated by an atmospheric general circulation model forced by the observed evolution of global SST and sea ice distributions as well as the direct radiative effects from both natural and anthropogenic sources. Contrasting this simulation with one forced by the observed SST and sea ice distributions alone reveals that the widening trend can be attributed entirely to direct radiative forcing, in particular those related to greenhouse gases and stratospheric ozone depletion. SST forcing causes no significant change in the width of the tropics, and even a contraction in some seasons.
In other words GHG emissions and emissions that cause ozone depletion are driving the expansion of the tropics. More worrisome though, is the growth in the area of the subtropics because this latter area is marked by deserts and extreme drought, some of the consequences of which we shall examine below.
The researchers conclude:
Taken together, the most likely culprits for the widening of the tropics since 1958 are increasing GHGs and stratospheric ozone depletion, both of which are of anthropogenic origin. Identification of their separate roles would require additional experiments with each radiative forcing agent considered individually.
Lu and Reichler’s work provides the theoretical background for the extreme drought conditions that are taking place around the world in places as diverse as Australia, California and Argentina.
According to the Independent:
Leaves are falling off trees in the height of summer, railway tracks are buckling, and people are retiring to their beds with deep-frozen hot-water bottles, as much of Australia swelters in its worst-ever heatwave.
On Friday, Melbourne thermometers topped 43C (109.4F) on a third successive day for the first time on record, while even normally mild Tasmania suffered its second-hottest day in a row, as temperatures reached 42.2C. Two days before, Adelaide hit a staggering 45.6C. After a weekend respite, more records are expected to be broken this week.
Ministers are blaming the heat – which follows a record drought – on global warming. Experts worry that Australia, which emits more carbon dioxide per head than any nation on earth, may also be the first to implode under the impact of climate change.
At times last week it seemed as if that was happening already. Chaos ruled in Melbourne on Friday after an electricity substation exploded, shutting down the city’s entire train service, trapping people in lifts, and blocking roads as traffic lights failed. Half a million homes and businesses were blacked out, and patients were turned away from hospitals.
More than 20 people have died from the heat, mainly in Adelaide. Trees in Melbourne’s parks are dropping leaves to survive, and residents at one of the city’s nursing homes have started putting their clothes in the freezer.
“All of this is consistent with climate change, and with what scientists told us would happen,” said climate change minister Penny Wong.
Meanwhile the Australian Broadcasting Corporation is reporting extreme temperatures in normally more temperate Tasmania:
The record for Tasmania’s hottest day was broken twice, with Flinders Island reaching 41 degrees on January 29th and Scamander 42 degrees the next day.
The record for Tasmania’s coldest January day was also broken, with Mt Wellington only reaching two degrees on the 16th.
A climate change expert from the University of Tasmania, Dr Kate Crowley, says it is very concerning.
“Shifting weather patterns cause shifting eco-systems so I guess that means areas that are dry are becoming wet, areas that are wet are becoming dry, areas that are prone to bushfire are going to be prone to catastrophic bushfire,” he said.
“So it really is of concern.”
This image from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite was captured on January 30. For larger image click here.
USA today reported that:
[Snow] Levels were 49% of normal in the northern Sierra and about 63% of normal in the central region and 68% of normal in the southern region.
California’s largest reservoirs — Shasta and Oroville — are less than half as full as they should be for this time of year. The snowpack water content needs to be roughly double what it is today by April to replenish the reservoirs, said Don Strickland, a spokesman for the water agency.
The immediate, economic consequences of this low snowpack are particularly worrisome given the already tenuous state of the economy. This from the Sacramento Bee:
[I]t’s easy for the experts to sound out a clear warning: This may become, simply, the worst drought California has ever seen.
“Our worst fears appear to be materializing,” said Wendy Martin, drought coordinator at the state Department of Water Resources. “It’s going to be a huge challenge.”
The bottom line, water officials said, is that right now, everyone must start using less water. The public can expect higher water bills and fines if they don’t, because the alternative is a real water shortage – one that is threatening tens of thousands of Valley jobs.
“It’s pretty scary,” said Tim Quinn, executive director of the Association of California Water Agencies, who has more than three decades in the water-supply business. “The public needs to tighten their belts. You have to rearrange all the molecules in your brain to think about using water differently.”
Researcher Richard Howett of UC Davis says that the immediate economic consequences could be enormous with losses of 40,000 jobs in the Central Valley alone and 1.15 billion in income. And that’s just in the farm sector.
Reports are that things are equally desperate in the Pampas region of Argentina
Earlier this week the Argentine government declared a drought emergency due to the ongoing drought crisis that is crippling the country’s key cattle, soy and wheat industries. Though normally dry because of the rain shadow created by the Andes Mountains to the west, the Pampas are receiving even less rain than usual and temperatures are unusually hot.
The Pampas region usually receives the bulk of its little rainfall during the summer months, between November and March. The rain in this region is absolutely necessary to maintain crop growth and for cattle grazing.
Corn production could be down up to 40 percent according to the latest estimates from the Buenos Aires Grains Exchange. 800,000 cattle have died in what the Argentine weather service is calling the worst drought in at least 35 years.
Dust Plume off Argentina’s Patagonian Coast south of Bahía Blanca by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite passed overhead. For larger image click here.
All this grim news comes on the heals of the publication of Susan Solomon’s paper on irreversible climate change, which forecasts centuries long droughts if we fail to take immediate action.
If CO2 is allowed to peak at 450-600 parts per million, the results would include persistent decreases in dry-season rainfall that are comparable to the 1930s North American Dust Bowl in zones including southern Europe, northern Africa, southwestern North America, southern Africa and western Australia.
The study notes that decreases in rainfall that last not just for a few decades but over centuries are expected to have a range of impacts that differ by region. Such regional impacts include decreasing human water supplies, increased fire frequency, ecosystem change and expanded deserts. Dry-season wheat and maize agriculture in regions of rain-fed farming, such as Africa, would also be affected.
1. The tropics are expanding, thereby increasing the desertification of large areas of the earth’s surface.
2. The extreme droughts we are seeing in Australia, California and Argentina are likely early signs of this phenomenon.
3. If we fail to act immediately and allow CO2 levels to reach the 450-600 ppm range we will most likely have condemned our descendants to a 1000 years of drought, and desertification of one third of the planet’s surface.
Crossposted at Daily Kos