Climate Change, Environment, Headlines, Latin America & the Caribbean, Tierramerica

CLIMATE CHANGE: Hot Days and Nights in Mexico 2090

Stephen Leahy* - Tierramérica

UXBRIDGE, Canada, Nov 20 2008 (IPS) - Climate change will dramatically increase the number of hot, dry days in Mexico in the coming decades, while coastal regions like the Yucatán, in the southeast, will be swamped by sea levels that are half a metre higher than today, a new study has found.

By 2030, Mexico's average daily temperature is likely to climb 1.4 degrees Celsius above what has been the average for the past 30 years. By 2090, this increase could rocket upwards by 4.1 degrees, virtually guaranteeing hot days and nights for 80 to 90 percent of the year, says the Oxford University study financed by the United Nations Development Programme (UNDP).

Cold weather will become very rare in Mexico according to data from the Intergovernmental Panel on Climate Change (IPCC), an umbrella organisation of scientists from around the world and the preeminent authority on climate change.

"Mexico is one area of the world where all the computer climate models agree," says Carol McSweeney of the School of Geography and Environment at Oxford.

Computer climate models incorporate the physics of the atmosphere and, often, the ocean, sea ice and land surface as well, to project what the future climate may be as carbon emissions from the burning of fossil fuels continue to rise, trapping more heat in the atmosphere.

The IPCC, co-winner of the 2007 Nobel Peace Prize, used the data from two dozen different climate models powered by the world's fastest supercomputers to issue its landmark Fourth Assessment Report last year.

That report warned the world that carbon emissions from the burning of fossil fuels are causing the current rise in global temperatures that could hike the global average temperature 4.5 degrees C by 2100.

But McSweeney and her Oxford colleagues wondered: what does that mean for individual countries? With UNDP funding, they have used the IPCC climate model data to determine the potential changes in the climate of 52 developing nations.

The study, presented Nov. 5, includes five Latin American countries: Cuba, Dominican Republic, Mexico and Nicaragua.

"We thought it was important to boil down all that complex data and create a summary report of what the data shows," McSweeney told Tierramérica.

In rare universal agreement, the highly complex models show Mexico will get much hotter and drier and that this will happen soonest in the north and central regions of the country, says McSweeney.

Climate change has already made the country warmer by about 0.6 C since 1960, according to the study. The number of hot days increased by 36 per year between 1960 and 2003.

Hot days are defined as the warmest 10 percent of the days over a 30-year span and are "what people normally would consider to be quite hot," McSweeney explained.

By 2060, one-third of all days will be "hot" by current standards, and by 2090 more than half the year will be like the hottest days of the year presently. On a regional basis, central and northern Mexico (including Mexico City) are projected to experience temperatures that are six and seven degrees higher than the current norm.

Cold days will be exceedingly rare by 2090 – perhaps just three or four days a year.

The main purpose of the study is to fill in the gaps of information of climate change in developing countries.

In Mexico, "it hasn't been easy" to provide climate information, and "we still can't completely rely on it," Juan González, coordinator of the doctoral programme in environmental law at the Autonomous Metropolitan University, told Tierramérica.

"The federal government and the states make measurements using different methodologies, and in many cases they aren't compatible," González added.

The Oxford study shows that the mean rainfall over the entire country has not changed since 1960, although there are wide regional variations. The number of intense or heavy rainfall events has increased by about 1.2 percent per decade.

But all models show a reduction in annual rainfall between three and 15 percent by 2090. Regional variations are difficult to predict because the models cannot simulate tropical cyclones, hurricanes or the cyclical El Niño/La Niña climate events, McSweeney pointed out.

"These projections must be used with caution and awareness of their shortcomings," she said.

Future regional rainfall estimates are one of those shortcomings, says Gavin Schmidt, a climate modeler at the NASA Goddard Institute for Space Studies in New York.

But Schmidt told Tierramérica that the UNDP/Oxford report "is a useful summary in terms of letting people in these countries know what is coming."

One other caveat is that these reports do not reflect sea level rise from climate change. The IPCC acknowledges that its data did not include the melting of the world's glaciers and ice sheets in the Arctic and Antarctic, says Schmidt, who is a member of the IPCC.

The ice melt is adding measurably to the sea level rise from thermal expansion of the oceans, he said. That is likely to mean greater impacts from ocean erosion and storm surges on flat, low-lying areas such as the Yucatán Peninsula, where the sea could rise as much as 56 centimetres.

The data also shows that in tropical and sub-tropical countries, warm season temperatures will be hotter than anything ever experienced previously starting as soon as 2050.

"It's important to understand that these will be unprecedented conditions," said Schmidt.

McSweeney hopes scientists and policy makers in Mexico review the report and send in their feedback or use the freely available IPCC climate model data to do their own analyses.

"We hope this is useful information, but further study is needed before making any policy decisions," she said.

The problem, said González, is that "Mexico still has short-term plans in which climate change is mentioned as a reference. There is no ambitious, realistic plan for developing alternative energy and changing course."

In fact, "a reform was just approved for the petroleum industry that reiterates the focus on development based on that finite, greenhouse-gas-generating sector," said González. Oil is Mexico's main source of revenues.

*With reporting by Diego Cevallos from Mexico City.

(*This story was originally published by Latin American newspapers that are part of the Tierramérica network. Tierramérica is a specialised news service produced by IPS with the backing of the United Nations Development Programme, United Nations Environment Programme and the World Bank.)