Changing weather patterns

“Since 1950, there has been 0.4 to 0.7°C warming, with more heatwaves, fewer frosts, more rain in south-west New Zealand, and less rain in north-eastern New Zealand. New Zealand is already experiencing impacts from recent climate change… These are now evident in increasing stresses on water supply and agriculture, changed natural ecosystems, reduced seasonal snow cover, and glacier shrinkage.”

– IPCC 4th Assessment on climate change impacts for New Zealand (2007).

While the quote is more than a decade old, the message remains the same: rising concentration of greenhouse gasses (GHG) in the atmosphere is changing weather patterns globally and locally. These GHGs trap heat in the atmosphere. More heat = more energy, turbo-charging atmospheric weather events and leading to ‘weather bombs’. Storms become more intense, so flooding is more frequent and intense. On the opposite end of the scale, droughts are harsher and evapotranspiration increases, affecting plants. Winter snowpack and glacial mass in New Zealand is decreasing rapidly, leading to a change in river flows.

In February 2018, temperatures in Siberia reached 35°C above average. In August 2019, the Greenland ice sheet was ‘in the throes of one of its greatest melting events ever recorded‘, while heat-driven wildfires broke out in Siberia and Greenland. These changes in temperatures alter the way global weather behaves, sometimes leading to unexpected outcomes, for example, the ‘wobble’ in the polar vortex leading to massive temperature swings across North America. A similar ‘wobble’ to the jetstream in the Southern Hemisphere also impacts the weather we experience in New Zealand.

The impacts of higher temperatures also affect the weather in the ocean, and with it, the oceanic food web.  What has now become known as a ‘marine heatwave’ was responsible for killing millions of fish, marine mammals, and seabirds in 2017. That affects the availability of food for river birds that depend on oceanic and coastal ecosystems over winter.

Marine heatwaves are now predicted to become the new normal.

NIWA: Our changing oceans, 13 June 2019

Why is it a problem for braided rivers?

From: ‘What does climate change mean for braided rivers?’ 2019 BRaid seminar.

Research and references

Below are references to material specifically used in this page or are of direct relevance. If you are interested in this topic, for the latest information we recommend Climate Central or the journal Nature Climate Change.