Its human nature to look for an easy solution to global warming. One such idea involves sprinkling tons of iron filings over the ocean to stimulate the growth of plankton that would consume carbon dioxide. Another involves spraying sun-blocking particles from aircraft into the stratosphere, mimicking the temporary cooling effects of strong volcanoes. Yet such mechanical escape hatches could be more trouble than they're worth. For example, it's unclear how the iron-filing approach would affect marine life and how long any benefits would last; and the cooling from a stratospheric shield wouldn't slow down the increase in atmospheric carbon dioxide or the acidification of oceans. Our planet's network of flora, fauna, oceans, ice and atmosphere is so integrated that surprises could easily result if we carry out global-scale tinkering, assuming that such a fix was even affordable. And as climatologist Stephen Schneider has pointed out, any unforeseen change in natural cycles could accentuate global warming just as easily as it might alleviate it.
It seems unlikely we'll escape a significant warming in the next century without making vast changes in the way we live. Even if we were to freeze the global output of greenhouse gases right away – a political and practical impossibility – we'd be in for some amount of warming, perhaps 0.5°C/0.9°F or more, simply due to the gases we've already emitted, their century-long lifespan in the atmosphere, and the extra heat already stored in our planet's oceans. In that sense, the choice before global society is how much additional warming we want to try to prevent. A number of environmental and policy groups have settled on a target of no more than 2°C/3.8°F beyond the pre-industrial global average. It's a goal they see as achievable through a gradual ramp-up in conservation, energy efficiency and new technologies, yet one low enough that it might prevent some of the more dire possibilities, such as wholesale extinctions or a collapse of the Atlantic conveyor-belt circulation.
As we face the hand we've dealt ourselves, there are several wild cards to take into account:
- The flip side of pollution At the same time that greenhouse gases act to warm us up, other industrial emissions help cool us down. Mainly, these are aerosols – tiny particles of dust, smoke, soot, and other stuff spewed out from cars, homes and factories, as well as volcanoes and large-scale fires. Aerosols act more like a shield than a greenhouse. They tend to reflect more energy than they absorb, which keeps some of the sun's rays from warming up the atmosphere (although new research is finding that soot may absorb more energy than previously thought).
The best guess is that aerosols cause about half as much cooling as greenhouse gases cause warming. But aerosols don't last long. Except for those thrown by volcanoes into the stratosphere (where they can cool global climate for one or two years), most aerosols stay in the air only a few days before falling out of the atmosphere. By contrast, the greenhouse gases produced by industry tend to stay airborne for decades. Because aerosols can't travel far during their short lifespan, their cooling tends to be concentrated near industrial centres, while most greenhouse gases are spread fairly uniformly around the entire world.
Aerosols induce respiratory disorders and damage our health in general, with the result that most industrialized countries are seeking to curtail them. Ironically, this could allow global warming to proceed at a faster pace. On the other hand, nobody knows how much developing countries like China will rely on coal burning and other aerosol-spawning technologies in the next century. This could have a huge effect on how and where global warming might be partially offset by aerosol cooling.
- What about the Sun? Until recently we only had crude knowledge of how much the energy put out by the sun varied from year to year. New instruments are now achieving far more precise readings of solar Irradlance (the amount of solar energy travelling to Earth) and how it varies. By correlating this data with visible sunspots, scientists have been able to use four hundred years of sunspot records to infer how the sun's output might have varied in the past. It now appears as if the cooldown in global temperature from about 1940 to 1970 coincided with a slight drop in solar energy. The temperature rises of 1900-1940 and 1970 into the twenty-first century seem to correspond to increases in solar energy.
To the best of our knowledge, however, these changes in solar energy aren't nearly enough to fully explain the temperature rise of the past century. Overall, it's estimated that we've seen at least three times more warming than would have resulted from solar variations alone. In other words, even if the Sun helped to sculpt the uneven shape of our century's temperature trend, there's been a temperature climb well above and beyond this factor, especially since the 1970s.
- Water and Ice The world's oceans are like an energy bank. Because it's so dense, water takes longer than air to warm up or to cool down. And the oceans have warmed up dramatically in the past hundred years. A study led by US oceanographer Sydney Levltus found far more warming than expected down to depths of 3000m/10,000ft, with half of the added energy stored above 300m/1000ft. Some of that heat may get transferred to the atmosphere in the coming years, whether through El Nlfio events, hurricanes or some less dramatic means. Nobody knows how quickly the oceans might release the heat they've stored.
Ice, on the other hand, helps to keep us cool. Sunlight is reflected easily from a bright ice patch or snow field. All else being equal, the more ice cover there is, the less solar energy gets absorbed by Earth and its atmosphere. Mid-latitude mountain glaciers have shrunk dramatically in the past century, but they represent only a small fraction of Earth's ice cover. Arctic sea ice is a different matter. The summertime thickness of Arctic ice has gone down by some 40 percent in the last fifty years, and the normal summer retrenchment of the ice pack's surface area has grown more extensive: some models now predict virtually ice-free Arctic waters in summer by the 2040s. The record-setting zone of summer melt in 2005 exceeded that of the 1978-2000 average by an area roughly twice the size of Texas. Glaciers across southern Alaska and Greenland are also melting at an increasing clip, a factor not fully accounted for in models of sea-level rise. Most of Antarctica remains ice-covered, but some ice shelves lining the West Antarctic Ice Sheet have been decaying, and a few spectacular collapses have been observed – most notably the Larsen В ice shelf. This floating ice mass attached to the Antarctic Peninsula lost an area of ice the size of Delaware to the sea in March 2002. Most of Antarctica's ice is expected to remain intact through the 21 st century and well beyond, but a substantial amount might be lost from the continent's western edges as warming proceeds.
- Greenery In 1992 a group of scientists teamed with the Western Fuels Association to produce The Greening of Planet Earth. This film – and a sequel, released in 1998 – made the case that greenhouse gas emissions might be a good thing: with increased carbon dioxide and warmer temperatures, plants would have a field day and society would benefit from it. As unyieldingly cheerful as the film's tone was, research has borne out some of its points. It does appear that extra carbon dioxide could be stimulating faster growth of some plants, although it's unclear what effect this might have on the plants' overall health and nutritive value and how other nutrients, such as nitrogen, might modify the plants'response. Also, the growing seasons in some places are becoming measurably longer. If agricultural interests were nimble enough to adapt to these changes, and if altered rainfall and snowfall patterns didn't get in the way, it's conceivable that the overall productivity of our planet's agriculture might increase – although, as climate boundaries shift, some countries could be winners while others would lose out Right now it appears that these shifts would favour northern countries like Canada and Russia while adding climatic stress to the poverty-plagued tropics.
Natural ecosystems will face their own challenges. A 2004 review of studies spanning a fifth of Earth's land areas found that up to 37 percent of plant and animal species could face extinction by the year 2050 if emissions increase at a modest pace. More than half of all species could be at risk if emissions climb more dramatically. Some animals and insects may be able to adapt to warming by simply migrating with the climate, but other species – some forest inhabitants, for instance – may not be able to shift poleward or otherwise adapt quickly enough. Forests themselves play a large part in determining climate. Trees are usually darker than open fields, and therefore tend to absorb more sunlight – but trees also ingest large amounts of carbon dioxide. During Kyoto negotiations, lobbyists from some heavily forested countries successfully argued that nations should get credit not only for planting forests, but also for maintaining existing ones.This could mean less pressure to reduce emissions.
The Kyoto Protocol wont come close to bringing the atmosphere back to its pre-industrial state – that would take centuries – and yet its goals are quite ambitious. By the year 2012, the original protocol called for an 8 percent cut in 1990 emission levels for the European Union, 7 percent for the US, and 6 percent for Japan and Canada, with lesser amounts for other nations. Such a plan might seem pie-in-the-sky, but there's a precedent for it. Following the discovery of the ozone hole above Antarctica, it took only two years for the world's countries (via the UN) to ratify the Montreal Protocol, which successfully called for a gradual replacement of the chemicals that were responsible for ozone depletion. For Kyoto, the implications and costs are far more widespread and the opposition was far stronger. Nonetheless, the protocol in its final, ratified form calls for emissions from industrialized nations by the year 2012 (except for the US, which opted out) to be reduced by an average of 5.2 percent over 1990 values – a requirement somewhat watered down from the original Kyoto draft, but still unprecedented.
Some of the biggest uncertainties that obscure the climate-change picture are human ones. For example, how will changes in technology and lifestyle affect emissions? Even though the US and Europe produced the lion's share of emissions in the 1900s, the developing world will likely take on that role sometime in the next several decades, if only due to population growth. Much will depend on whether growing economies fall back on older, dirtier technologies or incorporate greener ones. With the US acting as a role model for the high-consumption lifestyle, many developing countries feel they have the right to raise their standard of living just as their industrialized predecessors did. By the same token, many policy-makers (especially in the US) are loath to alter economies based on fossil fuels only to watch other countries burn the fuel they saved. The result is a global political picture that makes emissions cuts difficult to implement.
As the world begins planning for the next diplomatic steps to follow Kyoto, watch for a complex set of political manoeuvrings, both within and between nations. In the meantime, with the threat of serious climate change looming ever larger, many individuals and groups are taking action now. Alternative energy sources are on the increase: wind and solar power, which are virtually emissions-free, are each increasing by roughly 30 percent per year.
Research continues on more efficient forms of biofuels that are less reliant on petroleum-based farming techniques. Even nuclear power – which is free of carbon emissions, if environmentally problematic in other ways – is making a gradual comeback The big challenge will be addressing the use of coal, oil and natural gas. As developing countries grow, the global use of fossil fuels continues to climb. Even with the possible arrival of “peak oil” in the next few years, there's more than enough fossil fuel to produce truly worrisome climate change. That's especially true for coal, which is why cleaner ways of burning coal are a topic of intensive research.
Even if we could preserve today's climate under glass, Earth's increasing population adds to the risk of death and destruction from the weather calamities we already know too well Whether they set up housekeeping in paper-and-tin shacks or elegant mansions, people are flocking to homes near the sea – about two-thirds of the human race live within 160km/100 miles of a coastline – or in other weather-vulnerable locations. As political scientist, Roger Pielke Jr, has pointed out, once society has addressed these Achilles heels, we'll be better prepared for the future, no matter how severe climate change turns out to be.