Climate change update

A new report from the Office of Prime Minister’s Science Advisory Committee is on climate change. The forward has an extract worth noting:

An inherent feature of climate change science is its complexity and it must deal with many unknowns. Considerable research into the effects of greenhouse gases has been undertaken globally and, despite inevitable uncertainty, there is a very high scientific consensus regarding the likely magnitude, approximate timing of and the nature of the challenges ahead. It would be highly imprudent to ignore such projected scenarios just because they must be expressed in terms of probabilities rather than certainties. It is important to apply an understanding of uncertainty and of risk and their management to address this challenge and this means using the available and accumulating evidence appropriately. Just because there is an inherent level of uncertainty does not obviate the probability of impactful climate change and the need to be proactive in addressing it through mitigation and adaptive strategies.

The key policy issues are around how much focus one puts on mitigation and adaptation. Mitigation is preferable in theory, but in practice you need to get buy in from all the major emitters to make any significant difference. Adaptation however can be done nationally, and even locally. The report notes:

New Zealand’s net greenhouse gas emissions represent but a minute fraction of global emissions (less than 0.2%). Any action from New Zealand to mitigate emissions would have negligible direct global impact in real terms. Therefore, New Zealand’s contribution to the global effort to reduce greenhouse emissions is more of a geopolitical issue than a scientific one. Irrespective of what happens globally to emissions, the New Zealand challenge will involve adaptation to climate change.

The key projected changes for NZ are:

• Ocean acidification: pH changes are greater in cooler waters
• Temperature: The midrange of projections is an average temperature increase of 0.9°C by 2040, 2.1°C by 2090
• Wind: Increase in strongest winter winds by 2100
• Precipitation: Little change for the overall mean, but large geographical variation
• Extreme weather: Heavier and more frequent extreme rainfalls, but also more droughts. On average, 2 or more extra weeks of drought annually by mid-century for much of North Island and eastern South Island.

In terms of the recent temperature trends, the report notes:

• Over short time periods, natural variability has a significant impact on the global warming trend
• Short periods of no change or even slight cooling are to be expected, despite a continued long-term warming trend; 
• At times natural variability may even amplify warming;
• Global surface temperatures are only part of the picture, the ocean is a much larger heat sink than the atmosphere;
• The reported recent ‘hiatus’ in the rate of rise of temperature does not signal that climate change has ‘stopped’ or is no longer a concern

The report is around 20 pages long, and for my 2c is very well done. I suggest people actually read it, rather than jump to conclusions about what it does and does not say.