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Ka mua, ka muri – walking backwards into future

Farm machinery may have an ongoing reliance on fossil fuels. PHOTO/SUPPLIED


Chris Hollis

I am a geologist and paleontologist who, for the past 20 years, has been paid to investigate the geological context of climate change.

More specifically, my team has been tasked to find out how high greenhouse gas levels in times past have affected the plants, animals and environments of our region, the Southwest Pacific.

The aim is captured by the Māori whakatauki or proverb “Ka mua, ka muri” which means to use knowledge of our past to guide our future.

Anyone who pays attention to weather forecasts knows that predicting the future is hard.

There is a level of uncertainty even for tomorrow, let alone next week.

So, predicting the next 20 years, next 100 years, next 500 years is very hard indeed.

What can we say about climate change with some degree of certainty? Over the past 200 years, the level of carbon dioxide in the atmosphere has increased by 50 per cent and the global average temperature has increased by about one degree Celsius. That gives us an immediate clue to a key parameter when predicting the future: climate sensitivity.

This term refers to the relationship between the amount of carbon dioxide in the atmosphere and global warming, specifically, how much would the Earth warm if there was a 100 per cent increase [or doubling] of carbon dioxide? Based on the records from the past 200 years, we could say climate sensitivity is around 2C.

However, the past 200 years is just one short period in the 4.5-billion-year history of the planet. How do we know it’s truly representative of the future?

Turns out that if we plug the various permutations of the climate system into complex climate models, we get a much wider range of estimates of climate sensitivity – from 1.5C to over 5C.

This level of uncertainty should worry you if you are thinking about buying coastal property, considering which trees to plant on your farm or making long-term plans about water storage.

How about we walk backwards to the future and use the geological record of climate change to help reduce this uncertainty? Over the past few decades, we’ve developed a range of methods to reconstruct temperatures and carbon dioxide levels for the past 65 million years.

In studies of the last time we had carbon dioxide levels similar to today, around three million years ago, climate sensitivity comes out at about 3C.

That’s encouraging because it’s in the mid-range of climate model projections and means we can have some faith in them.

But it also means that many of the serious effects of global warming are already locked in and we need to urgently prepare for life on a planet where ice sheets are melting, sea levels are rising, both droughts and floods are more frequent, and a much more energetic climate system makes predicting the weather even more fraught.

For more on this, see the article “A degree of concern: why global temperatures matter” on Nasa’s website.

For Wairarapa, solutions relating to water storage, drought resistance and coastal erosion are essential.

To avoid our climate emergency becoming a climate catastrophe, we need to have pragmatic solutions to reduce emissions.

Vastly improved rail services for freight and commuters are essential.

Some ongoing reliance on fossil fuels must be factored in for a rural community where power outages may become more frequent and alternatives for farm machinery are still unavailable.

But that doesn’t mean we shouldn’t incentivise the use of alternatives where available and regulate the price and supply of petrol and other fossil fuels.

  • Chris Hollis lives with his family on a small farm on the Waingawa River. He is a research scientist at a Crown Research Institute, but the views expressed in this article are his own and may not represent the views of his employer.

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