Natural climate cycles usually play out over tens of thousands of years. Our species, however, has altered the natural climate trajectory of the planet in just 50, writes Professor Tim Naish who says the longer-term consequences of climate change are just as important as the short-term economic impacts.
Climate change is a global problem, and the world’s nations have agreed that global warming must be limited to less than two degrees celsius to avoid its most serious consequences. The science makes it quite clear that in order to achieve this target, global emissions of carbon dioxide need to be reduced to zero before the end the current century. Therein lies the challenge of our time.
Our government and 197 others are currently deciding on their intended contributions towards emissions reductions beyond 2020 for the United Nations climate negotiations in Paris later this year. As part of this process, the government has chosen to frame the discussion around short-term cost, and has been asking New Zealanders “what level of cost per household are we prepared to accept in order to reduce our greenhouse gas emissions?”
While many have expressed concerns about economic assumptions behind these costs, taken at face value they range from $1270 per household per year to achieve a five percent reduction below the 1990 target level by 2030, and up to $1800 for a 40 percent reduction.
But limiting the conversation to short-term costs avoids dealing with the much greater long-term consequences of missing the two degrees celsius target. The Intergovernmental Panel on Climate Change (IPCC) reports an upper limit sea-level rise of 1 metre above present day levels by 2100 if there is no emission reduction policy. It also acknowledges that higher sea levels are possible if parts of the Antarctic ice sheet behave unpredictably. The latest research shows that the United Nations Framework Convention on Climate Change’s (UNFCCC) target of 2C global warming is the threshold for the melting of Antarctic ice shelves—the parts of the ice sheet that flow into the ocean and provide a stabilising influence.
We have only recently discovered that 93 percent of the excess heat from anthropogenic global warming has gone into the ocean. If we exceed the 2C target then parts of the Antarctic ice sheet, including the highly vulnerable West Antarctic Ice Sheet, become unstable and continue to melt for many centuries to come. This will lead to more than the predicted 1 metre global sea-level rise by 2100, and many metres more further down the track. It is a sobering thought that approximately 200 million people live within 1 metre of present day sea-level.
As we consider our future contribution to greenhouse gas emissions reductions, it is important to remember that over and above a highly debatable cost per household, we may also be determining the future shape of our planet’s coastlines for centuries to come. Such large changes are usually driven by natural climate cycles that play out over tens of thousands of years. In just 50 years, however, our species has altered the natural climate trajectory of the planet.
The IPCC states that it is now virtually certain the Earth will not go into the next “ice age” if carbon dioxide levels stay above 400 parts per million—the current level in the atmosphere. So how much sea level rise, along with the other negative impacts of climate change such as droughts and floods, are we prepared to commit future generations to? What will be the real social and economic cost to New Zealand? What role should we expect our government to play in the guardianship of Aotearoa?
The longer-term impacts and costs of climate change must be given equal weight with short term issues as we, along with other nations, consider our contribution to the Paris negotiations.