ARC researcher’s role in IPCC report

Nick Golledge and two other Te Herenga Waka–Victoria University of Wellington scientists played key roles in the latest Intergovernmental Panel on Climate Change report, released on Monday.

Professor Nick Golledge
Professor Nick Golledge

Professor James Renwick, Head of Te Kura Tātai Aro Whenua–School of Geography, Environment and Earth Sciences, Professor Nick Golledge of Te Puna Pātiotio-Antarctic Research Centre, and Professor Dave Frame, the Director of the New Zealand Climate Change Research Institute, were all lead authors of chapters.

James was a lead author on the global water-cycle chapter, while Nick worked on the oceans chapter and Dave was a lead author on the chapter on the Earth’s energy budget, climate feedbacks, and climate sensitivity, and also a contributing author on the first chapter, on context and methods.

The Sixth Assessment Report (AR6) of the IPCC, which confirms that changes are happening in Earth’s climate across every continent and every ocean, took three years of writing and two weeks of virtual negotiations to approve.

In an article in The Conversation, Nick says Earth is now 1.09℃ warmer than it was in the 1850-1900 period.

“The assessment shows the ocean surface has warmed slightly less, by about 0.9℃ as a global average, than the land surface since 1850, but about two-thirds of the ocean warming has taken place during the last 50 years.

“We concluded that it is virtually certain the heat content of the ocean will continue to increase for the rest of the current century, and will likely continue until at least 2300, even under low-emissions scenarios.”

Carbon dioxide is the main driver of open-ocean acidification and marine heatwaves have doubled in frequency since 1980, becoming longer and more intense, he says.

The researchers have very high confidence that the amount of ice lost from West Antarctica in recent decades has exceeded any gain in mass from snowfall.

“We are also confident this loss has largely been due to increased melting of ice below sea level, driven by warming ocean water. This melting has allowed the acceleration and thinning of grounded ice further inland — and this is what contributes to sea-level rise.

“On the other side of the world, the Greenland ice sheet has also been losing mass over recent decades, but in Greenland this is principally due to warmer air, rather than warming ocean water.

“It is virtually certain that the melting of the two great ice sheets, in Greenland and Antarctica, as well as the many thousands of glaciers around the world, will continue to raise sea levels globally for the rest of the current century,” Nick says.

In an article for Newsroom, James says changes in the water cycle from climate change feature prominently in the latest report.

“As the climate warms, the water cycle has to respond. One of the main reasons is that the amount of moisture in the air is a function of temperature – warmer air holds more moisture (water vapour) – about 7% more for each 1°C of warming.

“So, when it rains, the chances are that the rainfall amount will be larger, just because there is more water to condense and fall out of the air.

“At the same time, in a warmer climate, evaporation works more effectively, so land surfaces dry out faster, allowing droughts to develop more quickly and to last longer.”

Variability and extremes in precipitation are increasing faster than changes in averages, he says.

“As the climate warms, the tracks of storms are moving towards the poles in many regions, notably across the Southern Hemisphere. At the same time, the high-pressure regions in the subtropics are expanding polewards.

“The net effects for New Zealand are that the west and south will see increases in precipitation in winter and spring, while the north and east will see reductions. Conversely, in the summer, the east is likely to see increases in rainfall while the west dries out a bit.”

Like elsewhere across the planet, New Zealand glaciers will keep retreating, James says.

Increased aerosols have helped offset the warming climate and have affected tropical monsoons and tropical rainfall more generally.

However, as the world cuts carbon emissions, and aerosols decrease in the atmosphere, the distribution of monsoon rainfalls will change.

“So, clearing the air is likely to lead to more floods and droughts, affecting very large populations.

“As we understand more about the water cycle, it is clear that all components are connected, and things are changing across the whole globe.

“There are no easy solutions to water availability, but it is clear that the sooner we stop emitting greenhouse gases, especially carbon dioxide, the sooner we stop the climate changing.

“That will make it easier for everyone to adapt, and to thrive,” James says.