The opportunity to limit the rise in average global temperatures this century to 2 degrees Celsius above pre-Industrial levels — corresponding to a CO₂ atmospheric concentration of 450 ppm — has pretty much slipped away, says climate scientist Robert Watson.

SAN FRANCISCO, CA, Dec. 5, 2012 — Renowned British climate scientist Sir Robert Watson pulled few punches today during a talk about the warmer world humans will face in coming decades.

Watson, who was IPCC chair from 1997 to 2002, all but dismissed the possibility of keeping the rise in average global temperatures to 2 degrees Celsius above pre-industrial levels — a temperature rise that corresponds to an atmospheric concentration of CO₂ of 450 parts per million. It now stands at about 390 ppm.

“Fundamentally, we are not on a path toward a 2 degree world,” Watson told a packed hall at Moscone Center for a talk entitled: “A World Where the Atmospheric Concentration of Carbon Dioxide Exceeds 450 ppm.”

If the international community wanted a world in which the rise in average global temperatures this century peaked at 2 degrees C above pre-Industrial levels, CO₂ emissions in the developed world should have peaked in 2010, Watson said. Globally, they would need to peak by 2014.

Instead, CO₂ emissions in 2010 were up 5.9 percent relative to 2009 — and that was in the midst of an economic downturn for most industrialized countries. Total carbon emissions as well as carbon intensity (often described as the amount of CO₂ emitted per unit of a nation’s GDP) have gone up.

“It’s totally clear we’re changing to composition of the atmosphere …” [but] “politicians have not listened to the scientific message,” Watson said.

Average global temperatures could rise 2 to 7 degrees C by the end of the century, driving a litany of environmental changes, Watson said. Already, the climate of the 2020s and 2030s already is locked in, or as Watson put it, “pre-ordained.” “Therefore, we must adapt,” he said.

In a quick moving lecture, Watson outlined several challenges the world will confront. Among them:

• Rainfall: Changes in precipitation are difficult to predict. Generally, a warmer atmosphere becomes loaded with more water vapor, but where it rains out is tough to estimate. Climate models generally show higher latitude regions and parts of the equator getting wetter, and the sub-tropics getting drier.
• Sea-level rise: The latest IPCC assessment, AR4, was criticized for underestimating how much sea levels could go up by 2100, and the forthcoming assessment should include more up-to-date information that more completely incorporates contributions from melting glaciers and ice sheets, particularly in Greenland. But Watson emphasized that rising sea levels will vary considerably from region to region. Tidal effects and variations in the globe’s gravity profile matter; Australia, for example, is expected to see much higher sea levels than the coast of South America. Globally, a one-meter rise on average is expected — “very significant for low-lying areas,” Watson warned. Once sea levels are rising significantly there’s a huge amount of inertia in the system “and it’s hard to slow it down,” he added. The notion of inertia in the climate system is a concept that governments “have not come to grips with,” Watson said.
• Melting ice: Watson offered some harrowing statistics, saying that 90 percent of the Greenland ice sheet was subjected to some amount of melting by early July — the highest percentage ever seen. The extent of Arctic sea ice, meanwhile, was not only the lowest ever seen this year, the thickness of the ice is also diminishing.
• Tropical storms: Some studies show that by 2100, there could be a doubling of Category 4 and 5 hurricanes in the Atlantic.
• Heat waves: Heat waves akin to ones that have scorched much of Europe in recent years are expected to become more common. Poor, undeveloped nations will be particularly vulnerable.
• Continued warming will devastate biodiversity around the globe, and climate change could become the primary driver for the loss of biodiversity.
• Ocean acidification: at an atmospheric concentration of CO₂ at 450 ppm, coral reefs stop growing, Watson said. At 550 ppm, they begin dissolving.
• Food: Get ready for higher food prices as warming temperatures stress rice, wheat, maize, soybean and other grain crops.
• Security: Tens of millions of people could be displaced by the effects of a warming world, where low-lying delta regions could become inundated, small island states drown, and shortages of food intensify.

The challenge of lowering greenhouse gas emissions won’t merely require a shift away from carbon intensive fuels and industry, Watson continued. Methane emissions from ruminants and rice production must be lowered, deforestation addressed and agricultural practices reformed.

Coal remains the dominant single source of energy worldwide, but natural gas — while extracted by controversial “fracking” techniques — could reduce the global dependence on coal. Still, Watson said, “it’s not a solution; it may (only) buy us a bit of time.”

Developed nations also have to come to grips with their carbon footprint — and an accounting that includes “embedded carbon” generated by their consumption of goods produced in carbon-intensive nations such as China.

While listing the familiar steps needed to decarbonize the world economy — a shift away from carbon intensive fuels, higher fuel efficiency, the development of renewables and nuclear power, placing a price on carbon through emissions trading or taxation, and mobilizing behavioral change — Watson appeared skeptical about the prospects, at least in the near term.

“The only way to get to a 2 degree world is to de-carbonize immediately, and I see no political signs we’re doing this …. We need moral leadership and political will, and they are in short supply.”