Navigating uncharted waters

Preventive measures such as the London flood barriers will not work long-term. Picture / Getty Images.

The science is now unequivocal - climate change is unprecedented in recent human history. Even if we substantially reduce greenhouse gas emissions in coming decades, there is inbuilt momentum in the climate system that will lead to significant changes this century.

That means adapting is imperative and the challenge is more complex than simply predicting and responding to impacts.

According to the recently-released Inter-governmental Panel on Climate Change (IPCC) report, New Zealand is already experiencing higher temperatures, more hot extremes and fewer cold extremes, and shifting rainfall patterns in some regions.

By 2100 the IPCC expects global sea levels to have risen by up to 1m above the 1986-2005 average in a high carbon scenario - and it could be much higher. We could experience increases of up to 10 per cent higher than the global average.

Though it's not possible to make precise local predictions for sea level at the end of the century, it's clear levels will rise for many centuries to come given our current greenhouse gas emissions. But the rate and scale will depend on future emissions.

With so many communities located at the coast, sea-level rise poses a serious risk in New Zealand. Climate change will also have a significant impact on our freshwater supply and ecosystem health, and low-lying coastal areas and floodplains will become prone to flooding and erosion.

Given projected patterns of development and population distribution, the combination of sea-level rise and increasingly heavy rainfall in some regions is especially concerning. At particular risk are low-lying ecosystems, massive public and private investment in exposed areas, public safety, community resilience and livelihoods, and an array of traditional Maori assets and practices.

Many NZ communities are taking steps to adapt to climate change but efforts to address sea-level rise, for example, can be ad hoc, contentious and prone to costly litigation.

IPCC analysis shows our capacity to adapt is constrained by widely vary-ing attitudes towards climate risk, and what constitutes appropriate adaptation. There is limited capacity at the local level to assess risks, and poor integration between government at the local and national levels, and with the private sector and public.

Heavy rain caused flooding to parts of the upper North Island. Photo / Brett Phibbs

Adaptation planning is challenging for communities because it is often framed as a technical problem that can be solved by science. Yet science can't provide precise answers about the impact of climate change because of the complexity of the climate system and the inherent 'unknowability' of long-term changes.

We are often too focused on responses that draw "a line in the sand", but climate change is progressive and layered with uncertainty; it requires flexible responses.

Protective seawalls and stopbanks can reduce the risk for communities located in places prone to erosion and flooding, but can become unviable if the risk escalates over time. Relying on these structures can also result in a cycle of protection, development, increased protection, and further development.

This cycle can be disastrous if an extreme event exceeds the design standards, as in New Orleans after Hurricane Katrina. So, while large barriers may be a necessary short to medium-term option for protecting key infrastructure such as airports and major rail and roading networks, they may not be the way forward as sea level rises. They are definitely not the long-term answer.

What's really key to climate change adaptation planning is the process for communities to make decisions. They need an effective forum for weighing up the costs, benefits and risks of different scenarios and deciding where future development should and should not take place.

They need a process to decide which assets and eco-systems should be protected in the short-term, what can be done to mitigate the effects of extreme events in the medium-term, and how to resolve competing interests when the only sensible option is to retreat.

These are tough, expensive questions with no easy answers. It's a process that requires legislative reform, a shift in mindset and new approaches to planning. It means accepting climate change is already happening and that it will progress in unpredictable ways - and that it's not a technical problem to solve, but a set of political decisions to be made.

• Bruce Glavovic, holds the EQC Chair in Natural Hazards Planning at Massey University