Sometimes warnings pack more punch when they come in a concentrated form – and at the right moment.
That's the hope United Nations officials have expressed after the weekend release of the last of four reports this year on global warming and options for trying to bring it under control.
The report reflects rising scientific confidence – and remaining uncertainties – in describing current and projected effects of global warming. That, plus the report's condensed size and terse talking points, virtually ensure it will play a key role in adding urgency to negotiations that begin on Dec. 3 in Nasu Dua, on the island of Bali in Indonesia.
The aim of next month's meeting is to gain consensus on a formal framework for reaching a new emissions-reduction pact over the next two years. A new pact would pick up where the 1997 Kyoto Protocol leaves off. Currently it only requires industrial countries to reduce their greenhouse-gas emissions by an average 5.5 percent below 1990 levels between 2008 and 2012.
Over the weekend, delegates from 140 nations meeting in Valencia, Spain, adopted the Intergovernmental Panel on Climate Change's (IPCC) "synthesis report." It's a thin volume distilled from three larger tomes the UN-sponsored group of scientists, economists, and other experts released earlier this year. It draws no new conclusions. But it does insist that some effects of global warming, such as sea-level rise, are inevitable and will continue for centuries, even if all heat-trapping greenhouse-gas emissions stopped tomorrow. Heading off the worst of the effects means moving aggressively to curb rising greenhouse gases, mainly carbon dioxide from burning fossil fuels, the report suggests.
The message "could not be simpler," says UN Secretary-General Ban Ki Moon. "Global, sweeping, concerted action is needed now; there is no time to waste."
The synthesis report reiterates that the warming of Earth's climate is "unequivocal" and that the scientists involved express "very high confidence" that human activities have warmed the climate since 1750. It also indicates that human influence on climate has contributed to rising sea levels, shifting storm tracks, increasing temperature extremes, and raising the risk of heat waves, droughts, and heavy rains.
The synthesis report uses sea levels to illustrate what many see as unavoidable long-term effects, depending on the rate of warming.
Even the most aggressive scenario to curb greenhouse-gas emissions – with emissions peaking by 2015 and falling to between 50 and 80 percent of 2000 levels by 2050 – would still warm the planet enough to ensure that over the next millennium, global average sea level would rise by up to 4.6 feet. The least aggressive scenario, which yields the largest warming, would raise sea levels by up to 12 feet. These increases come merely from heating the oceans, which expand when warmed. The scenarios don't take into account meltwater that icecaps in Greenland or Antarctica would contribute as the global average temperatures rise.
The concentration of carbon dioxide in the atmosphere needed to hold sea-level rise to a minimum "is basically where we are right now," says Ronald Stouffer, a researcher and a member of the synthesis report's core writing team. But global average temperatures today do not yet reflect "in any way, shape, or form, the amount of carbon dioxide and other greenhouse gases in the atmosphere," he says, because of the inertia in the climate system.
Trends in carbon-dioxide emissions hint at the tough job that awaits negotiators heading for Nasu Dua, Indonesia next month. A team of government and university scientists from Australia, the US, Britain, France, and Austria reported in late October that between 2000 and 2006, carbon dioxide concentrations in the atmosphere grew at the fastest rate since monitoring began in 1959. Some two-thirds of the increase comes from industrial emissions and deforestation, the researchers note. But, they add, another 18 percent can be traced to oceans and plants, which are becoming less efficient at soaking up CO2. Computer models the IPCC uses to track Earth's natural carbon cycle have projected a slowdown in CO2 uptake by oceans and plants. According to the team, the slowdown is larger and is coming earlier than models project. CO2 concentrations are at their highest level in at least 650,000 years and likely the last 2 million years, the team noted.
Criticism that the IPCC process is too political often comes from conservative groups. They argue that the worriers have hijacked the IPCC process, leading to a litany of gloomy scenarios.
However, concern about politics and the IPCC process also comes from some scientists, who argue that because the IPCC operates by consensus among the political delegations who must approve the reports the scientists produce, the reports may understate the challenges humanity faces from global warming.
The reports, which appear every five to six years, represent a snapshot of the science that is now about two years old, notes Dominique Bachelet, an associate professor in the biological and ecological engineering department at Oregon State University in Corvallis, Ore. "The climate is changing so fast," and while the authors are writing and assembling the reports, "science is moving on."
The synthesis report and its progenitors serve as a highly useful baseline, she says, "but it's a conservative baseline."
Despite the challenges, the UN's Mr. Ban says he remains optimistic that countries can agree. "I'm encouraged by the level of political will.... I look forward to China and the US to play a more constructive role" at Bali. "Both can lead."