Tim Naish: If emission talks focus only on short-term costs, we will pay dearly

We may be determining the shape of our planet's coastlines for centuries to come. Photo / Nasa

Climate change is a global problem, and the world's nations have agreed global warming must be limited to less than 2C to avoid its most serious consequences. To achieve this target, global emissions of carbon dioxide need to be reduced to zero before the end of this century. Therein lies the challenge of our time.

Our Government and 197 others are deciding on their 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 framed the discussion around short-term cost, asking "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 5 per cent reduction below the 1990 target level by 2030, and up to $1800 for a 40 per cent reduction.

But limiting the conversation to short-term costs avoids dealing with the much greater long-term consequences of missing the 2C target. The Intergovernmental Panel on Climate Change (IPCC) reports an upper limit sea-level rise of 1m 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.

We have only recently discovered that 93 per cent 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 become unstable and continue to melt for many centuries. This will lead to more than the predicted 1m global sea-level rise by 2100, and many metres more further down the track. It is a sobering thought that around 200 million people live within 1m of present-day sea level.

As we consider our contribution to emissions reductions, we must remember that beyond a highly debatable cost per household, we may also be determining the 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, we have altered the natural climate trajectory of Earth.

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 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 consider our contribution to the Paris negotiations.

• Professor Tim Naish is director of the Antarctic Research Centre at Victoria University of Wellington.