Scientists have just put together New Zealand’s 150 years of climatic history, revealing a cool spell fueled by volcanic eruptions – and an increasing footprint of climate change. Photo / Leon Menzies
Scientists have just put together New Zealand’s 150 years of climatic history, revealing a cool spell fueled by volcanic eruptions – and an increasing footprint of climate change.
A team of researchers has compared land temperatures recorded across the country between 1871 and 2019 with data on surrounding sea levels, finding that our wider region has warmed by about 0.66C during that time.
Most of the heat has come in over the last few years, due to global warming.
“Although there were some very warm years in the early 1970s, all of the warmest years have occurred since 1998,” said the study’s lead author, Professor Jim Salinger.
The new study offers a deeper picture than our official record for tracking national temperature trends – the “seven stations” series – consisting of ground-based measurements that have been carried out continuously since 1908.
Salinger, the original architect of the seven-station series, says New Zealand has one of the best and oldest temperature records in the world, starting from the groundwork of Sir James Hector and colleagues in the 1860s.
“What we’re doing here is pushing the record back, as well as updating it to 2019,” he said.
“We want to cover the larger area of New Zealand, not just the land, because we are dealing with the four million square kilometers that are home to fisheries and other parts of our economy.”
Using a series of data sets, Salinger and colleagues took a thorough look at what drove our coldest and warmest periods.
They found two large natural drivers that dominate the trend are the inter-decade Pacific oscillation (IPO) and the south-El Nino oscillation (ENSO).
Both show major cyclical changes in the Pacific oceanic system, which in turn affect our own climate.
When an IPO is in a negative phase, for example, New Zealand tends to get more northeast and northeast, as well as warmer temperatures.
ENSO – seen in between El Nino, neutral, and La Nina states – also carries a mixed effect.
While La Niña years show above-average temperatures with more of the northeast, El Nino years usually prove cooler than average, due to more southwestern winds.
Another natural influencer is something called the Southern Annular Mode (SAM) – a ring of climate variability that surrounds the South Pole, but stretches deep into our own latitudes.
Several warm years have been put in the SAM that is locked in a mostly positive phase, which comes with further southerly westerly winds over the southern oceans but lighter winds and brighter skies over New Zealand.
Salinger said this kind of trend has been increasing recently.
Surprisingly, the massive eruptions have left their fleeting tracks, spewing massive amounts of dust and sulfate aerosols into the atmosphere.
Records show how local temperatures dropped slightly after six major blows, including Krakatoa in 1883, Tarawera in 1886 and Mount Pinatubo in 1991.
“We found out how this could mean temperatures fell about 0.3C to 0.5C lower than some of the previous season – and there seems to be a lot more southwest.”
Even more striking, Salinger said, are the real trends emerging with climate change.
This paper finds our coolest years to have occurred before 1933.
Between 1870 and 1895, temperatures ran about 0.4C below the 1981-2010 average, then, in the early 1900s, fell further to 0.8C below that baseline.
Temperatures also felt cooler in the early 1930s, and then 0.4C below the 1940s average, and were generally near normal during the 1950s, 1970s and 1980s.
While they fell again to about 0.5C below normal in the early 1990s – partly due to the Pinatubo eruption – they rapidly increased to 0.1C above normal, before averaging 0.4C above normal throughout the 2010s.
When this trend comes together with natural drivers who have historically made for more comfortable conditions, New Zealand experienced very warm years.
One example is our warmest year on record – 2016 – which coincided with set-up pressures that pushed more north and northwest across the country.
But study co-author and leading climate scientist Professor James Renwick, of the University of Victoria, points out that other human-driven effects have also changed our climate.
“The fact that we have a trend toward a positive southern annular mode – which is linked to the ozone hole, to a large extent – also adds to the warming over the past 50 years,” he said.
“That effect will probably weaken as the ozone hole starts filling up, helping to halt the trend in SAM.
“New Zealand will continue to warm in the future, but the rate of warming that we will see over the rest of this century may actually be a little slower than we have seen over the last 50 years.”
Globally, emissions are expected to continue to increase – meaning increased, acidifying oceans and more weather events such as major storms, droughts and heat waves.
At current levels, global average temperatures are likely to cross the 1.5C threshold above pre-industrial levels in the next 10 to 20 years.
And a 3C increase by the end of this century is projected, even if all current emission reduction commitments and goals are met by the international community.
Massive cuts in net emissions will be needed to hold warming to 1.5C – about 45 percent below 2010 levels by 2030, and net zero by around 2050.
The research team – which also includes Dr Howard Diamond, of the US National Oceanic and Atmospheric Administration – dedicates the paper to the late Niwa climate scientist, Dr Brett Mullan, whose decades of work have been pivotal.