Daily Bulletin

The Conversation

  • Written by Kale Sniderman, Senior Research Fellow, School of Earth Sciences, University of Melbourne

As the planet warms, subtropical regions of the Southern Hemisphere, including parts of southern Australia and southern Africa, are drying. These trends include major drought events such as Cape Town’s “Day Zero” in 2018.

Read more: ‘Day Zero’: From Cape Town to São Paulo, large cities are facing water shortages

Climate projections suggest this subtropical drying will continue throughout the 21st century. Further drying in these regions will place great stress on ecosystems, agriculture and urban water supplies.

Our new study, published today in Nature Climate Change, suggests the subtropical Southern Hemisphere drying trend may reverse, if global temperatures stabilise in a future world with zero net greenhouse gas emissions.

Dry places get drier, wet places get wetter

As global temperatures increase, some regions get wetter while others get drier. Climate models indicate that many parts of the tropics, where it is already very wet, will become wetter. The subtropics, which sit between the wet tropics and the wet mid-latitudes, are expected to get drier.

Slowing climate change could reverse drying in the subtropics Spatial plot of global rainfall projections for 2100 from IPCC AR5, showing percent change in annual rainfall for each °C of global warming, for the last two decades of the 21st century relative to 1986-2005. Subtropical regions, like the Mediterranean and southern Australia are projected to dry. Modified from IPCC AR5 Ch. 12 Fig 12.10

Over southern Australia, rainfall is expected to decline, particularly in the cool season (which is currently the rainy time of year). This has already happened in Perth and the surrounding southwest of Western Australia.

Slowing climate change could reverse drying in the subtropics The drying trend in South-west Western Australia over the last century is significant. BoM

What will happen when warming slows or stops?

Climate models are typically used to explore future climate under transient or rising temperatures, at least until the end of the 21st century. International efforts to reduce greenhouse gas emissions are aimed at slowing and eventually stopping temperature rises so that the climate is stabilised. For example, the Paris Agreement aims to stabilise global warming within 1.5℃ or 2℃ above pre-industrial levels.

But if temperatures stop rising, how will rainfall patterns respond? To investigate, we used pre-existing climate model runs created by the international scientific community to project different conditions extending from the present to the year 2300.

The chart below shows two different scenarios: one in which greenhouse gases and temperatures level off around 2100 (this referred to as Extended Representative Concentration Pathway 4.5), and the one next to it (Extended Representative Concentration Pathway 8.5) in which greenhouse gases don’t level off until around 2250, creating a much warmer climate.

Slowing climate change could reverse drying in the subtropics Smoothed global temperature and subtropical (25°S-35°S) winter (June through August) rainfall in Extended Representative Concentration Pathway (ECP) 4.5 and ECP8.5, from 2006 to 2300. Author provided

We found that rainfall in the Southern Hemisphere subtropics decreases while temperatures are rising rapidly, with most of the rainfall reduction occurring in the winter months. When temperatures begin to stabilise, subtropical rainfall starts to recover.

How rainfall reversal works

The subtropics are relatively dry right now because they are the region where dry air descends from the upper atmosphere to the surface, suppressing rainfall. Studies have shown that the subtropics may be expanding or shifting southward in the Southern Hemisphere as the global climate warms.

Our study found a link between the trend in Southern Hemisphere subtropical rainfall and the temperature gradient between the tropics and subtropical regions. This temperature gradient gets steeper during periods of rapid warming because the tropics warm faster. Once warming stops, the regions further from the Equator catch up and the temperature gradient gets weaker.

The pattern of temperature warming drives the shifts in rainfall: when the tropics are warming faster, the subtropics become drier as more moisture is exported to the tropics.

Read more: The world's tropical zone is expanding, and Australia should be worried

A wetter or drier future?

Our results suggest that stabilising global temperatures may lead to a reversal in the drying trend in the subtropics.

The path to stabilising global temperatures will be a long journey from the current trajectory of rising emissions, but this research is potentially good news for the future generations who will live in subtropical regions.

The authors would like to acknowledge Nathan P. Gillett, Katarzyna B. Tokarska, Katja Lorbacher, John Hellstrom, Russell N. Drysdale and Malte Meinshausen, who contributed to this study.

Authors: Kale Sniderman, Senior Research Fellow, School of Earth Sciences, University of Melbourne

Read more http://theconversation.com/slowing-climate-change-could-reverse-drying-in-the-subtropics-111526


The Conversation

Politics

Prime Minister on the Alan Jones Show

ALAN JONES: Prime Minister, good morning.    PRIME MINISTER: Good morning Alan, how are you? Good to hear you back on the air.   JONES: Thank you. Thank you very much. Can I just - there's a lot...

Alan Jones - avatar Alan Jones

The Greens side with activists, not farmers

The Greens’ Agriculture Spokesperson, Senator Janet Rice, today made some disgraceful comments in relation to the Government’s tough new penalties for keyboard warriors who incite activists to inv...

Senator Bridget McKenzie - avatar Senator Bridget McKenzie

Scott Morrison interview with Alan Jones - 2GB

ALAN JONES: The Prime Minister's on the line from Melbourne, Prime Minister good morning. PRIME MINISTER: Good morning Alan ALAN JONES:  thank you for your time. I wish we had three hours but look...

Alan Jones - avatar Alan Jones

Business News

Top 5 Reasons Businesses Are Shifting From Magento To Shopify

Although building an online business has been made simpler by the extensive use of the internet, maintaining its success is a journey rather than a destination. It involves critical decisions made a...

News Company - avatar News Company

Deliveroo appoints Laura Huddle as Head of Commercial in Australia

Leading online food platform Deliveroo has appointed Laura Huddle as Head of Commercial in Australia, as the platform continues to invest in building a strong and experienced local leadership team...

Sinead Harding - avatar Sinead Harding

The Most Successful Start-Ups in Australia

The future looks bright for Australia’s start-up sector. Cities like Sydney, Melbourne and Perth are beginning to be recognized as most popular Australian start-up hubs. More and more companies are ...

News Company - avatar News Company

Travel

DEAL: Kids stay and eat for FREE these school holidays!

Take these school holidays to the next level with the ultimate family escape at PARKROYAL Darling Harbour. What’s more, kids under 12 years of age, can stay and eat for FREE! ...

Liana Gardy - avatar Liana Gardy

How to Book a Hotel for Your Vietnam Trip

Finding a travel destination may turn out to be challenging at times. You may have a long bucket list, which leaves you spoilt for choice on where to visit first. Going through travel blogs and site...

News Company - avatar News Company

New Allianz data reveals the ‘forgotten’ European countries attracting Australian travellers this winter

FROM SPAIN TO THE UKRAINE - THE SURPRISE EUROPEAN DESTINATIONS BOOMING WITH AUSSIE TOURISTS Australian travellers are seeking new destinations beyond the Mediterranean when it comes to European...

Media Release - avatar Media Release

ShowPo