Key Takeaways
- La Niña conditions and background climate change trends combined to create the intense rainfall that devastated North Island communities
- Sea surface temperatures globally have steadily increased, leading to more moisture in the atmosphere and heavier rainfall
- New Zealand’s mountainous terrain contributes to the intensity of rainfall events
- Climate experts warn that the country can expect more extreme rainfall events due to rising ocean temperatures
- Reducing net greenhouse gas emissions to near-zero can halt further changes, but reversing the current climate conditions is unlikely without advanced technology
Introduction to Climate Change and La Niña
La Niña conditions and background climate change trends have been identified as the primary causes of the intense rainfall that has devastated North Island communities in recent times. According to climate experts, the combination of these two factors has led to an increase in extreme weather events, resulting in significant damage and disruption to affected areas. Even before the most recent bout of heavy rain, monthly rainfall in certain regions, such as Northland, the Coromandel, East Cape, and Gisborne, was already sitting at between two to four times the usual amount. This trend is expected to continue, with climate experts warning that the country can expect more extreme rainfall events due to rising ocean temperatures.
The Role of Sea Surface Temperatures
Dr. Kevin Trenberth, a distinguished scholar at the US National Centre for Atmospheric Research and an affiliate of the University of Auckland physics department, explains that sea surface temperatures globally have steadily increased by about half a degree. This increase in temperature leads to more moisture in the atmosphere, largely through evaporation, resulting in heavier rainfall. When the flow of air out of the tropics targets New Zealand, the amount of rain that falls can be 20 to 30 percent more than what would have been received in the 1970s. The middle map shows how rainfall this January has varied, compared to the long-term average, with some areas experiencing significantly more rainfall than usual.
Regional Climate Patterns
The sea north of New Zealand is particularly warm at the moment, with temperature spikes of one to two degrees above normal for this time of year, according to Trenberth. This warmth tends to attract convection, showery conditions, and anything weather-wise that’s heading in that direction tends to get amplified. There is often a seasonal pattern to where storms tend to track, and this can last for two or three months. The second and third storms are particularly problematic because the ground is already saturated, leading to increased flooding and damage. Earth Sciences New Zealand chief climate scientist Sam Dean notes that New Zealand’s mountainous terrain does not help, as it causes moisture to be carried by storms and then dropped as rainfall when they interact with the hills.
Climate Change and Extreme Weather Events
La Niña conditions have prevailed over the last decade, making it difficult to separate out climate variability from longer-term patterns. However, climate experts believe that they are seeing more extreme rainfall events occurring, and this is one of the consequences of climate change for a country like New Zealand. Victoria University climate science professor James Renwick warns that the kind of weather events New Zealand is experiencing on a regular basis had long been warned of. As oceans warm, warmer air can hold more moisture, leading to heavier rainfall, which is the climate change trend. The warming and sea level rise that have already occurred are locked in for centuries, and if the world could reduce net greenhouse gas emissions to near-zero, that could halt further changes.
Adapting to Climate Change
To cope with the changes that are already occurring, New Zealand needs to continue its efforts to adapt communities threatened by severe weather. This is happening in some places, and it is very much down to individual regional authorities. However, the country now has a National Adaptation Plan, and hopefully, more adaptation responses will be seen over the next few years. Renwick notes that it gives him no pleasure to say, "I told you so," but the kind of weather events New Zealand is experiencing had long been warned of. The country needs to take proactive steps to mitigate the effects of climate change and adapt to the new reality. By reducing greenhouse gas emissions and implementing adaptation strategies, New Zealand can reduce the impact of extreme weather events and create a more resilient and sustainable future.