Dr Harrington presented on climate change in Aotearoa through the lens of academic research, revealing what can be understood from models and studies whilst also discussing the limitations of using our current body of knowledge to make predictions about the effects of climate change on our extreme weather events.

How are things changing? Research on seven cities in New Zealand shows there have been notable increases in temperature in the last five years, with many more days above the “usual” seasonal temperature.

Why are things changing? It seems clear that cumulative Greenhouse Gas emissions are the cause. As cumulative emissions increase, so do temperatures. There is a linear relationship!  As long as we keep emitting, temperatures will increase. We cannot just reduce emissions and expect temperatures to stabilise as cumulative emissions are the key. Thus the concept of “net zero” is crucial.

How tough is the challenge to reach net zero? New Zealand has committed to reach net zero by 2050 but is already behind! Our carbon budget is likely to be very tight as 2050 approaches!

Dr Harrington discussed how rising temperatures might impact weather events in New Zealand.

1.    Cyclone Gabrielle was more intense (more rain) due to climate change

Extreme weather conditions caused insured losses of $250 million in 2020, rising to $350 million in $2022. Gabrielle and the Auckland Anniversary flooding caused $2 billion insured losses between them!

Comparing Met Service predictions with actual rainfall (a “highly conditioned analysis”) and comparing with pre-industrial climate, it appears that 10% more rain is falling in our warmer climate. In the future, assuming a 2° temperature rise, rainfall would increase by another 10%. The rainfall will also become more intense, but for shorter periods.

2.    Although we may not have more ex-tropical cyclones in future, they will be more intense

There is no clear evidence that the frequency of tropical cyclones will increase. However, more will reach a higher category, so 20-30% more rain will fall from them.

 3.    The impact on the incidence of agricultural drought

 We still don’t know whether summers will be wetter or dryer in the future – a fundamental question and “really annoying” that we don’t know.

 As the climate becomes warmer, a “getting wetter” model predicts that increased rainfall will be offset by an increase in evapotranspiration.

 A ”getting dryer” model suggests that there will be less water topping up the soil and even though there will be less evapotranspiration the soil moisture deficit will increase.

 4.    Looking at the past is still important to understand what the future might be

 Dr Harrington suggested that Waikato is statistically overdue for a significant drought!

 The most recent droughts, in 2007-08 and 2012-13, were both followed by an unusually wet April. However, if a similar drought were to be followed by a “normal” April, this would be scary!

 5.    Heat extremes are changing rapidly – faster than we thought.! We don’t talk about heat enough! – perhaps because Australia is hotter?

 The latest IPCC* report places New Zealand last in terms of countries getting hotter! Dr Harrington believes that this is incorrect, as we have so many microclimates which are not accounted for in the IPCC studies.

 New Zealand models suggest that in future, three out of four summers could see what we now consider to be a “once-in-a-decade” period of high temperatures.

If temperatures continue to increase, we can expect more heatwaves, including perhaps 5-day periods of temperatures in the mid-30s.

*IPCC Intergovernmental Panel on Climate Change

 Conclusion

We understand the causes of temperature change and its effect on the severity of rainfall, but we don’t know whether our summers will be wetter or dryer.

Extreme drought (in Waikato) and severe heat are to be expected.

How would our lives be affected in circumstances such as more intense heatwaves? – we should plan for all contingencies!

 A questioner asked whether the research findings could be made more precise/local and the language used by climate change scientists be made more accessible and relevant.

In response, Dr Harrington explained that there is a balance between certainty and precision. Although it would be good to let everyone know what the climate and extreme weather will be like in each of their properties, such predictions are not possible at present and are not likely in the near future.