Climate explained: will the tropics eventually become uninhabitable?

Flickr/, CC BY-NC-ND

James Shulmeister, University of Canterbury


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What is the impact of temperature increases in the tropics? How likely is it that regions along the Equator will be uninhabitable due to high wet bulb temperatures such as 35℃ and more in places like Singapore? Do we have models that suggest how likely this is and at what time frames?

More than 3.3 billion people live in the tropics, representing about 40% of the world’s population. Despite some areas of affluence, such as Singapore, the tropics are also home to about 85% of the world’s poorest people and are therefore particularly susceptible to the impacts of climate change.

The tropics are expected to experience rising temperatures and changes to rainfall, and the question is whether this could make this region uninhabitable. How would this happen?

Heat stress

Humans regulate their body temperature in warm conditions through sweating. The sweat evaporates and cools the skin. But if conditions are humid, sweating and evaporation are much less effective.

Humans can survive and function in quite high temperatures if humidity is low, but as humidity increases our ability to function decreases rapidly. This effect is measured by a heat stress index which shows the apparent temperature you feel under different relative humidity conditions.

From a human health point of view, the wet bulb temperature is critical. This is the temperature a thermometer covered in a wet cloth would measure, and it reflects the maximum amount of cooling that can be achieved by evaporation.

High wet bulb temperatures are more problematic to human health than high absolute temperatures. Wet bulb temperatures above 35℃ are life-threatening because they cause hyperthermia, which means the body cannot cool down and the internal body temperature exceeds 40℃.

Climate modelling predictions used by the Intergovernmental Panel on Climate Change (IPCC) for the period from 2080-2100 suggest warming in the tropics of about 1.6℃ under mid-range emissions scenarios and up to 3.3℃ under high emissions scenarios, with error margins of about 0.5℃ on both predictions.

Read more:
Siberia heatwave: why the Arctic is warming so much faster than the rest of the world

Different parts of the world respond in different ways to warming from greenhouse gas emissions. The projected warming in the tropics represents about 40% of the expected temperature rise in the Arctic.

High-latitude regions – far north or south of the Equator – warm more rapidly than the global average because excess heat in the tropics creates a temperature and pressure gradient. This drives heat up to higher elevations and higher latitudes through an atmospheric circulation called the Hadley cell.

The stronger the gradient, the more heat is exported.

Hot in the city

There is one additional factor: urbanisation. Singapore is a good place to look at actual climate change in the tropics.

A Singapore skyline with clouds and some sun breaking through.
Cities such as Singapore will get hotter.
Flickr/Mohammad Hasan, CC BY-NC

Records from Singapore indicate temperatures have increased by 1.1℃ over 42 years to 2014. This is nearly twice the average global rate of warming over recent decades and is opposite to expectations.

The difference appears to be due to a heat island effect caused by the city itself. This is important because changes in land use amplify background global climate change and put tropical cities at greater risk of extreme heat. As populations are concentrated in cities, this increases the risk to human health.

The mean average temperature for Singapore is about 27℃, whereas Jakarta in Indonesia is slightly warmer. At the scale of predicted mean annual temperature change, neither of these cities would become uninhabitable. But even a small temperature increase would make life more challenging.

This is made worse in at least some parts of the tropics, because total rainfall is increasing, suggesting a long-term rise in humidity. For example, average rainfall in Singapore increased by more than 500mm from 2,192mm in 1980 to 2,727mm in 2014.

Read more:
Urban growth, heat islands, humidity, climate change: the costs multiply in tropical cities

Deadly heat

People working outdoors are at higher risk, as are vulnerable populations, including the elderly. Under the IPCC’s high-emission trajectory, heat-related deaths in Jakarta in August are expected to rise from about 1,800 in 2010 to nearly 27,000 in 2050.

People unloading cargo in the outdoors at Jakarta port.
Working outdoors in the increased heat and humidity will get harder.
Flickr/Jorien, CC BY-NC

Even allowing for a significant increase in elderly people as the Indonesian population ages, this means about 15,000 excess deaths in this month. Estimates under high-emission predictions for the tropics and mid-latitudes suggest about a 40% decline in the ability to undertake manual work during the warmest month by 2050.

These impacts will be stronger in the seasonally wet tropics (such as the Northern Territory of Australia), where more extreme warming is expected than in the equatorial zone.

Predictions for Darwin, in northern Australia, suggest an increase in days with temperatures above 35℃ from 11 days a year in 2015 to an average of 43 days under the mid-range emission scenario (IPCC’s RCP4.5 scenario) by 2030 and an average of 111 (range 54-211) days by 2090. Under the higher emission scenario (IPCC’s RCP8.5), an average of 265 days above 35℃ could be reached by 2090.

In summary, while absolute temperatures are expected to rise more slowly in the tropics when compared with higher latitudes and polar regions, the combination of heat and rising humidity will make life challenging, but not impossible.The Conversation

James Shulmeister, Professor, School of Earth and Environmental Sciences, University of Canterbury

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Why blowing the 1.5C global warming goal will leave poor tropical nations sweating most of all

File 20180529 80650 hogx79.jpg?ixlib=rb 1.1
Poor tropical nations are likely to feel the effects of climate change most acutely.

Andrew King, University of Melbourne and Luke Harrington, University of Oxford

Almost all of us are going to be worse off as climate change takes hold, whether through heatwaves, changing rainfall patterns, sea level rise, or damage to ecosystems. But it’s the world’s poorest people who will suffer the biggest disruptions to their local climate, as our new study, published in Geophysical Research Letters today, explains.

The Paris Agreement aims to keep global warming well below 2℃ above pre-industrial levels, and ideally no more than 1.5℃. Meeting the more ambitious 1.5℃ target will be extremely challenging, given that we have already had more than 1℃ of global warming so far, and global greenhouse emissions are still rising.

Read more:
Fossil fuel emissions hit record high after unexpected growth: Global Carbon Budget 2017

We examined the likely consequences of missing the 1.5℃ global warming target in terms of perceptible local climate change, by looking at the “signal-to-noise ratio”. The idea is that 1℃ of warming is more noticeable where there is very little variation in temperature (such as in Singapore, for example) compared with places where the temperature variations are much higher (like Melbourne). Where temperature variations are smaller less warming is needed before the change in climate becomes noticeable.

Read more:
Ground zero for climate change: the tropics were first to feel the definite effects in the 1960s

Society and ecosystems are adapted to the range of temperatures experienced in their location, so the signal-to-noise measure of climate change reflects this effect. In simple terms, it is a measure of how soon global warming will push the temperature beyond the normal bounds of variation at a given location. This will happen sooner in places where the weather doesn’t vary much, and later in places where it does.

Because global warming is likely to overshoot the ambitious Paris goal of 1.5℃, but perhaps not the more modest 2℃ goal, we looked in particular at the signal-to-noise ratio created by using state-of-the-art global climate model projections to move between 1.5℃ and 2℃ of global warming.

More perceptible warming is projected over the tropics than at higher latitudes.
CREDIT, Author provided

As expected, the signal-to-noise ratio is high in the tropics, where the variability in temperature is lower. This means that local temperature changes due to global warming will generally be felt more keenly in the tropics than at higher latitudes if the world exceeds the 1.5℃ Paris target.

The inequality of climate change

Next, we overlaid the signal-to-noise ratio data with population and gross domestic product (GDP) data to investigate the relationship between local climate change and wealth.

As the less economically developed areas of the world are predominantly in the tropics, and the more developed economies are at higher latitudes, we predict that the world’s wealthiest countries will experience less perceptible climate change than the poorest.

Locations in the poorest countries tend to experience greater local climate change.
Author provided

For example, we project that the people of the UK, the first country to industrialise and one of the world’s richest nations, would experience less than half the level of perceptible climate change, as measured by our signal-to-noise ratio, than the people of the Democratic Republic of Congo, one of the world’s poorest.

This means that if we do exceed the 1.5℃ Paris target, the countries that will face the biggest impact are those who are least to blame for creating the problem, and least equipped to deal with the resulting problems.

Read more:
Developing countries can prosper without increasing emissions

An impetus to act

Keeping global warming to modest levels, as signatories to the Paris Agreement have pledged to do, has many benefits compared with the alternative of a 3℃ or 4℃ warmer world. Previous research has shown that this would reduce the frequency of heat extremes and their impacts in many places around the world, and would reduce droughts and extreme rain events. There would be benefits for many of the world’s plant and animal species as well as entire ecosystems, including the Great Barrier Reef.

Limiting global warming also helps the poorest parts of the world develop. By reducing greenhouse gas emissions more rapidly the developed world would put less of the burden of climate change onto the developing world. This should incentivise stronger emissions reductions globally. The UN Sustainable Development Goals call for action to eradicate absolute poverty and reduce inequality. Our research underlines the fact that both of these goals, and others, depend implicitly on reining in global warming.

The ConversationUnfortunately, the alternative – and where our current emissions trajectory is taking us – is a warmer world in which the poorest and least culpable nations pay the biggest price.

Andrew King, Climate Extremes Research Fellow, University of Melbourne and Luke Harrington, Postdoctoral Research Assistant, Environmental Change Institute, University of Oxford

This article was originally published on The Conversation. Read the original article.

The world’s tropical zone is expanding, and Australia should be worried

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‘Tropics’ may conjure images of sun-kissed islands, but the expanding tropical zone could bring drought and cyclones further south.
Pedro Fernandes/Flickr, CC BY-SA

Steve Turton, CQUniversity Australia

The Tropics are defined as the area of Earth where the Sun is directly overhead at least once a year — the zone between the Tropics of Cancer and Capricorn.

However, tropical climates occur within a larger area about 30 degrees either side of the Equator. Earth’s dry subtropical zones lie adjacent to this broad region. It is here that we find the great warm deserts of the world.

Earth’s bulging waistline

Earth’s tropical atmosphere is growing in all directions, leading one commentator to cleverly call this Earth’s “bulging waistline”.

Since 1979, the planet’s waistline been expanding poleward by 56km to 111km per decade in both hemispheres. Future climate projections suggest this expansion is likely to continue, driven largely by human activities – most notably emissions of greenhouse gases and black carbon, as well as warming in the lower atmosphere and the oceans.

If the current rate continues, by 2100 the edge of the new dry subtropical zone would extend from roughly Sydney to Perth.

As these dry subtropical zones shift, droughts will worsen and overall less rain will fall in most warm temperate regions.

Poleward shifts in the average tracks of tropical and extratropical cyclones are already happening. This is likely to continue as the tropics expand further. As extratropical cyclones move, they shift rain away from temperate regions that historically rely upon winter rainfalls for their agriculture and water security.

Researchers have observed that, as climate zones change, animals and plants migrate to keep up. But as biodiversity and ecosystem services are threatened, species that can’t adjust to rapidly changing conditions face extinction.

In some biodiversity hotspots – such as the far southwest of Australia – there are no suitable land areas (only oceans) for ecosystems and species to move into to keep pace with warming and drying trends.

We are already witnessing an expansion of pests and diseases into regions that were previously climatically unsuitable. This suggests that they will attempt to follow any future poleward shifts in climate zones.

I recently drew attention to the anticipated impacts of an expanding tropics for Africa. So what might this might mean for Australia?


Australia is vulnerable

Australia’s geographical location makes it highly vulnerable to an expanding tropics. About 60% of the continent lies north of 30°S.

As the edge of the dry subtropical zone continues to creep south, more of southern Australia will be subject to its drying effects.

Meanwhile, the fringes of the north of the continent may experience rainfall and temperature conditions that are more typical of our northern neighbours.

The effects of the expanding tropics are already being felt in southern Australia in the form of declining winter rainfall. This is especially the case in the southwest and — to a lesser extent — the continental southeast.

Future climate change projections for Australia include increasing air and ocean temperatures, rising sea levels, more hot days (over 35℃), declining rainfall in the southern continental areas, and more extreme fire weather events.

For northern Australia, changes in annual rainfall remain uncertain. However, there is a high expectation of more extreme rainfall events, many more hot days and more severe (but less frequent) tropical cyclones and associated storm surges in coastal areas.

Dealing with climate change

Adaptation to climate change will be required across all of Australia. In the south the focus will have to be on adapting to projected drying trends. Other challenges include more frequent droughts, more warm spells and hot days, higher fire weather risk and rising sea levels in coastal areas.

The future growth of the north remains debatable. I have already pointed out the lack of consideration of climate change in the White Paper for the Development of Northern Australia.

The white paper neglects to explain how planned agricultural, mining, tourism and community development will adapt to projected changes in climate over coming decades — particularly, the anticipated very high number of hot days.

For example, Darwin currently averages 47 hot days a year, but under a high carbon emission scenario, the number of hot days could approach 320 per year by 2090. If the north is to survive and thrive as a significant economic region of Australia, it will need effective climate adaptation strategies. This must happen now — not at some distant time in the future.

This requires bipartisan support from all levels of government, and a pan-northern approach to climate adaptation. It will be important to work closely with industry and affected local and Indigenous communities across the north.

These sectors must have access to information and solutions drawn from interdisciplinary, “public good” research. In the face of this urgent need, CSIRO cuts to such research and the defunding of the National Climate Change Adaptation Research Facility should be ringing alarm bells.

The ConversationAs we enter uncharted climate territory, never before has public-good research been more important and relevant.

Steve Turton, Adjunct Professor of Environmental Geography, CQUniversity Australia

This article was originally published on The Conversation. Read the original article.

EcoCheck: Australia’s Wet Tropics are worth billions, if we can keep out the invading ants

Steve Turton, James Cook University

Our EcoCheck series takes the pulse of some of Australia’s most important ecosystems to find out if they’re in good health or on the wane.

The largest area of tropical rainforest in Australia – the so-called Wet Tropics – is a narrow strip along the northeast coast of the continent, totalling about 2 million hectares.

It represents just 0.26% of the continent, but is crammed with hugely diverse landscapes: rainforests, sclerophyll forests, mangrove forests and shrublands, as well as areas of intensive agriculture and expanding urban rural population centres.

The Wet Tropics bioregion and World Heritage Area.
Peter Bannink/Australian Tropical Herbarium, Author provided

The Wet Tropics are home to a dizzying array of plants and animals. These include at least 663 vertebrate species, 230 butterflies, 135 different dung beetles and a remarkable 222 types of land snail. The area is teeming with more than 4,000 plant species, including 16 of the world’s 28 lineages of primitive flowering plant families.

In all, the Wet Tropics bioregion contains 185 distinct ecosystems. Of these, 18 are officially listed as endangered and 134 are of conservation concern.

Wild riches

Just under half of the region is covered by the Wet Tropics of Queensland World Heritage Area, the world’s second-most-irreplaceable natural world heritage area. A recent analysis listed it as the planet’s sixth-most-irreplaceable protected area in terms of species conservation, and its eighth-most-irreplaceable when considering only threatened species.

Yet despite its global conservation significance, the Wet Tropics was recently described by the International Union for the Conservation of Nature (IUCN) as a World Heritage Area of “significant concern”.

This is due to the threat posed to the area’s biodiversity and endemic plants and animals by invasive species, diseases and predicted climate change impacts. Only two other Australian world heritage properties are listed as “of concern”: the Great Barrier Reef and Kakadu National Park.

Given these concerns, one might expect research dollars to be flowing towards the Wet Tropics. In fact, the opposite is happening: the new National Environmental Science Program has pledged a paltry A$10,000.

Commonwealth funding for Wet Tropics research under successive programs: the CRC for Rainforest Research; the Marine and Tropical Sciences Research Facility (MTSRF); and the National Environmental Research Program (NERP). Under the National Environmental Science Program, only $10,000 has been allocated (not shown).
Rainforest CRC; MTSRF; NERP; CRC Reef Synthesis Report; Reef & Rainforest Research Centre, Author provided

While we’re talking money, it’s worth pointing out that the Wet Tropics are a goldmine. In its 2014-15 report, the Wet Tropics Management Authority calculated that this natural global asset is worth a whopping A$5.2 billion each year – roughly half of it from tourism.

A 2008 report found that the Wet Tropics create the greatest economic benefit of any of Australia’s natural world heritage properties, excluding the Great Barrier Reef. It found that every dollar spent on management costs earned an A$85 return in tourism spending. Even in purely economic terms that makes a pretty compelling case for conservation.

Climate and conservation

But there are question marks over the Wet Tropics’ future, not least because it is considered a hotspot for impacts from climate change. This is primarily due to the very large predicted declines in range size for almost all of the vertebrates that are unique to this part of the world, such as the iconic lemuroid ringtail possum. Climate change is likely to force some species to shift their geographic ranges, or face extinction.

Many of the species at greatest risk of extinction from climate change are confined to higher elevations and thus have very limited scope for dispersal. Of all the rainforest vertebrate species in the Wet Tropics, 30% live within the coolest 25% of rainforest. This gives them nowhere to go if things warm up. For unique species, that figure is even higher, with 45% living in these cooler areas.

Nor is the future too bright for many mountaintop plants, according to a study that modelled the future of suitable climate conditions for 19 species found only above 1,000 m elevation.

The study predicted that, by 2080, 84% of these species would have no suitable habitat anywhere in the Wet Tropics, and so would no longer be able to survive there.


Watch out for these crazy guys.
John Tann/Wikimedia Commons, CC BY

The climate isn’t the only problem. Another is the accidental introduction of one of the world’s worst invasive species, yellow crazy ants, into two locations in the Wet Tropics.

Judging by the ants’ impacts elsewhere, this is an impending natural catastrophe. Based on the small amounts of research in the region so far, ecologists Lori Lach and Conrad Hoskin predict that a large invasion of yellow crazy ants could affect most of the animal species in the Wet Tropics.

These impacts could be direct – through predation and harassment – or indirect, such as by the removal of invertebrate prey or disruption of processes such as decomposition, pollination and seed dispersal. The potential for knock-on effects in a system as complex and interconnected as the Wet Tropics rainforest is very high.

We have only a small window of opportunity – perhaps five years at most – to keep the Wet Tropics safe from yellow crazy ants. The cost of failure by the Australian and Queensland governments is unimaginable. Yellow crazy ants are also a threat to agriculture and urban areas, so we should anticipate a successful and properly funded eradication campaign — mirroring the papaya fruitfly eradication efforts in the same region back in the mid-1990s.

If the siege can be repelled, we can hopefully go on enjoying the Wet Tropics – not to mention the money it generates – for many years to come.

Are you a researcher who studies an iconic Australian ecosystem and would like to give it an EcoCheck? Get in touch.

The Conversation

Steve Turton, Professor of Environmental Geography, James Cook University

This article was originally published on The Conversation. Read the original article.

Tropics: Wildlife Populations Collapsing

The link below is to an article reporting on the crisis for wildlife populations in the tropics where wildlife populations have crashed by 61% in the last 50 years.

For more visit: