Tag Archives: tropics

Too Hot in Texas

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New modelling of climate change effects on mosquito populations in the United States has surprising results – it might get too hot in summer even for the mosquitoes

WHO: R A Erickson, S M Presley, Department of Environmental Toxicology, and Institute of Environmental and Human Health, Texas Tech University, Lubbock, Texas
K Hayhoe, Department of Political Science, Texas Tech University, Lubbock, Texas
L J S Allen, Institute of Environmental and Human Health, and Department of Mathematics and Statistics, Texas Tech University, Lubbock, Texas
K R Long, Department of Mathematics and Statistics, Texas Tech University, Lubbock, Texas
S B Cox, Department of Environmental Toxicology, and Institute of Environmental and Human Health, Texas Tech University, Lubbock, Texas and Research and Testing Laboratory, LLC, Lubbock, Texas

WHAT: Population modelling for the Asian Tiger mosquito which carries dengue fever under two climate change scenarios

WHEN: 5 July 2012

WHERE: Environmental Research Letters, Vol. 7, No. 3 (July-Sept 2012)

TITLE: Potential impacts of climate change on the ecology of dengue and its mosquito vector the Asian tiger mosquito (Aedes albopictus)

This group of researchers in Texas decided it would be interesting to look at different climate change emissions scenarios from the IPCC and see what the effect of climate change might be on everybody’s ‘friend’ the Asian Tiger mosquito. For those of you who haven’t met the Asian Tiger mosquito, it is the type that carries dengue fever, which makes you very sick. So understandably, how climate change affects the population spread of this mosquito is pretty important.

The Asian Tiger mosquito is not your friend (Wikipedia)

The researchers looked at three localised areas in the US to run their model – Lubbock TX (where their University is), Atlanta GA, and to look at the potential geographical spread of the mosquito; Chicago IL.

Many of the predicted consequences of climate change are currently happening decades ahead of schedule, and one of the consequences is the expansion of the tropical belt by around 2- 4.8o latitude since 1979. This wasn’t expected to occur until 2100, so it means mosquitoes could be moving north faster than previously predicted.

The climate scenarios used were the A1FI (high emissions) and B1 (medium emissions) from the IPCC Special Report on Emissions Scenarios, which relate to approximately 970ppm (A1FI) and 550ppm (B1) of CO2 in the atmosphere. To give some context for those numbers, we’re currently sitting at 391ppm. 550ppm is where feedback loops have already kicked in and there are large ocean ‘dead zones’ where there’s not enough oxygen for plant and animal life. 970ppm is the IPCC’s ‘worst case scenario’ where there is mass biodiversity loss and a high likelihood of mass extinction events.

IPCC Emissions Scenarios A1FI (above) and B1 (below)

Anyway, back to mosquitoes. The researchers used three of the world’s best and most detailed climate models; the CM3 model from the UK’s Hadley Centre, the National Centre for Atmospheric Research model in Colorado, and the National Oceanic and Atmospheric Administration’s CM2.1 model. They used the mean temperature data from their three locations and combined it with the climate model to work out what the average temperatures might look like under the scenarios. Then they applied those conditions to mosquito populations to see what might change.

What they found was very interesting, and not what the researchers had originally expected. While the population size and duration of the mosquito season in Chicago increased across the board along with the potential dengue fever outbreak size, in Lubbock and Atlanta the mid-summer temperatures got too hot even for the mosquitoes.

Chicago (left) and Lubbock (right) with mid and end of century predictions. Chicago has an increase in mosquito population while Lubbock has a noticeable mid-summer die-off of mosquitoes (from paper)

While the mosquito season in Lubbock started earlier and had a potential for greater dengue fever outbreaks, the super-hot summer temperatures under both of the climate change scenarios modelled led to mosquitoes dying and a reduction in potential dengue fever outbreaks. This could have many social and health policy ramifications in the areas studied and also shows that the local level effects of climate change may manifest in ways we haven’t previously thought of.

Humans are notoriously difficult to predict and we don’t know yet what humanity will do about climate change in the near future. This gets combined with natural systems and feedbacks that are highly integrated and complex which means one seemingly unrelated process may be triggered in another previously unrelated process.

However, complexity doesn’t mean that models aren’t relevant or useful and the proverbial baby should be thrown out with the bathwater. Models give us a range of possibilities to plan for and allow humans the opportunity to act in our own long term best interests.

Currently, we’re not acting for our long term well being, and humanity is currently burning carbon at a rate that matches or beats the A1FI high emissions scenario that very probably leads to mass extinction, including humans. Which means that now would be the time to stop burning fossil fuels. Before Texas becomes so scorching hot that even the mosquitoes die from the mid-summer heat.

Predicting the Unpredictable: Tropical Hydrology

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Unpredictable tropical storms from climate change and changing land-use patterns are going to mess with water cycles

WHO:  Ellen Wohl (Department of Geosciences, Colorado State University, Fort Collins, Colorado)
Ana Barros (Duke University, Pratt School of Engineering, Durham, North Carolina)
Nathaniel Brunsell (Department of Geography, University of Kansas, Lawrence, Kansas)
Nick A. Chappell (Lancaster Environment Centre, Lancaster University, Lancaster, UK)
Michael Coe (Woods Hole Research Center, Falmouth, Massachusetts )
Thomas Giambelluca (Department of Geography, University of Hawaii at Manoa, Honolulu, Hawaii )
Steven Goldsmith (Department of Geography and the Environment, Villanova University, Villanova, Pennsylvania)
Russell Harmon (Environmental Sciences Division, ARL Army Research Office, North Carolina)
Jan M. H. Hendrick (New Mexico Institute of Mining and Technology, Socorro, New Mexico)
James Juvik (Department of Geography and Environmental Studies, University of Hawaii-Hilo, Hilo, Hawaii)
Jeffrey McDonnell (Department of Forest Engineering, Resources, and Management, Oregon State University, Corvallis, Oregon)
Fred Ogden (Department of Civil and Architectural Engineering, University of Wyoming, Laramie, Wyoming)

WHAT: Looking at what we know about tropical water patterns and working out what we don’t know

WHEN: September 2012

WHERE: Nature Climate Change, Vol 2 Issue 9, September 2012

TITLE:  The hydrology of the humid tropics (subs. req)

This paper from Nature Climate Change does two things; it looks at what we know about tropical water cycles (hydrology) and also the gaps in our knowledge (scientists- always wanting to know more!).

So what do we know?

Firstly, let’s define the ‘tropics’. This paper looks specifically at the humid tropics which is anywhere that precipitation exceeds evaporation 270 days a year or more, and is generally 25⁰ latitude either side of the equator.

The tropics highlighted in red (Wikipedia)

Fun fact – the tropics is where the term ‘the doldrums’ comes from. It’s officially known as the ‘Intertropical Convergence Zone’ and is the area where the winds coming from the northern hemisphere and the southern hemisphere collide, creating erratic weather patterns and violent thunderstorms. This poses a few issues in the face of climate change. Climate change will make weather more extreme and the effects will be non-linear, so this means the tropics are about to get even less easy to predict.

There are many areas of the tropics where land-use changes are affecting water cycles. Deforested areas outnumber the remaining forest, which is already having a measurable effect on rain patterns in Brazil; extending the dry season and rain being more intense when it does occur. It’s estimated that deforestation in the South Eastern Amazon has increased the flow of water to the ocean by 20% in the last 40 years. These changes and others will likely be amplified with increased climate change effects.

Billions of people rely on the major rivers in the tropics for their fresh water, and flows of water, energy and carbon are all closely linked to the amount and age of vegetation in the area. Changes in water flows and rain patterns can be disastrous, and can occur from combinations of land-use change, deforestation and climate change. So messing with the systems can create large changes. The closely linked relationship between vegetation type and water cycles also means that my idea of trying to grow an Australian gum tree here in Vancouver when I feel homesick is a bad one.

However, while water cycles are being modified across the tropics by land-use changes, deforestation and climate change, the effects are going to vary region by region, making predictions difficult. There are far fewer weather measuring stations in tropical areas than temperate areas, so less data overall. The researchers identified moisture cycling, water catchment processes and long term data collection as areas that need improvement if we are going to be able to accurately predict global warming changes in the tropics.

Number of weather stations in temperate vs tropical areas (from paper)

In order to answer important questions that relate to the availability of fresh water for billions of people and extreme weather in areas that have earthquake activity as well as cyclones there needs to be a detailed body of data. Forewarned is forearmed, especially if systems are heading towards possible tipping points, and this paper would like researchers to study more tropical areas to better understand them.