The full impact of the greenhouse gases already in the atmosphere will not be felt until around 2050. If greenhouse gas emissions stopped immediately, that date is when Earth would reach a new stable state, with a new climate. That’s because of the long life of CO2 in the atmosphere. Researchers call this ‘the commitment’: change we are yet to feel but can’t prevent.
Much of the CO2 released when people stoked their coal-fuelled stoves in the aftermath of World War I is still warming our planet today. Most of the damage was done starting from the 1950s, when people drove about in their fin-tailed Chevrolets and powered their labour-saving household appliances from inefficient coal-burning power stations.
It is the baby-boomer generation born in the years following World War II that is most to blame: half of the energy generated since the Industrial Revolution has been consumed in just the last twenty years.
It’s easy to condemn this extravagance, but we must remember that until recently nobody had the slightest idea that their auto emissions or electric vacuum cleaner would have an impact on their children and grandchildren.
But now we know. The true cost of your family’s four-wheel-drives, air conditioners, electric hot water services, clothes dryers and refrigerators is increasingly evident to all. In many developed nations we are three times as affluent on average as people were a few decades ago, and therefore we are able to bear the cost of changing our ways.
Our commitment—the climate change we can no longer prevent—is influenced by a number of factors:
• the CO2 we have already released;
• the positive feedback loops that amplify climate change;
• global dimming;
• the speed at which human economies can decarbonise themselves.
The first—existing greenhouse gas volumes—is known and cannot be changed.
The second and third—positive feedback loops and global dimming—are still being explored by scientists.
And the fourth—the rate at which we humans can reduce our emissions—is being argued over right now in parliaments and boardrooms around the world. It and global dimming are the only impacts over which we have control.
Scientists say that a 70 per cent reduction in CO2 emissions from 1990 levels by the middle of the twenty-first century is required to stabilise Earth’s climate. This would result in an atmosphere with 450 parts per million CO2— remember it’s now at 380 parts per million. Our global climate would stabilise by around 2100 at a temperature at least 1.1°C higher than the present, with some regions warming by as much as 5°C.
The European nations are talking of emissions cuts on this scale but, given the resistance of the coal industry and the policies of the Bush and Howard administrations in the US and Australia, this may not be an achievable target. A more realistic scenario may be 550 parts per million of atmospheric CO2—double the pre-industrial level. This would result in climatic stabilisation centuries from now, and an increase in global temperature of around 3°C this century.
But remember that even this depends on good luck. The level of greenhouse gases already in the atmosphere may trigger positive feedback loops with the potential to cause change we can’t control.
It’s too late to avoid altering our world, but we still have time to avoid disaster and to reduce the probability of dangerous climate change.
Perhaps a more useful way of looking at the problem is to work out rates of change that are dangerous. After all, life is flexible, and if given sufficient time it can adapt to the most extreme conditions. But if change occurs too quickly, plants and animals won’t have time to adapt. If we think about it this way, warming rates above 0.1°C per decade are likely to cause grave damage to our ecosystems. Similarly, rates of sea level rise above two centimetres per decade would be dangerous, as would a rise of five centimetres overall.
But the question of what constitutes dangerous climate change raises another question—dangerous to whom? For the Inuit in the Arctic a damaging threshold has already been crossed. Their primary food sources of caribou and seal are now difficult to find as a result of climate change and their villages are under threat.
When we consider the fate of the entire planet, there can be no illusions about what is at stake. Earth’s average temperature is around 15°C, and whether we allow it to rise by a single degree, or 3°C, will decide the fate of hundreds of thousands of species, and billions of people.