Global warming: even a rise of 2 ° C has disastrous consequences

Even if the world manages to limit warming to 2 ° C, the consequences for biodiversity and humanity will be disastrous, alert scientists who detail several scenarios.

Even if temperatures stabilize at + 1.5 ° C or + 2 ° C, the sea level will continue to rise by 90 or 120 cm by 2300.

Rising seas, loss of biodiversity, complicated access to food, declining standard of living ... Even if the world manages to limit warming to 2 ° C, the consequences will be disastrous, according to about 20 studies published on 2 April 2018 in the British journal Philosophical Transactions of the Royal Society A. " We detect significant changes in climate impacts for a world at 2 ° C, so we must take steps to avoid it, " said AFP Dann Mitchell, of the University of Bristol, lead author of the text that introduced this special issue.

More than two years after the signing of the Paris agreement, which aims to keep the rise in the thermometer under 2 ° C, or even 1.5 ° C, compared to the pre-industrial era, the 20 or so studies are comparing the impact of both scenarios. " One of the challenges is how quickly we will reach + 2 ° C, " says Mitchell. In other words, the time that the world will have or not to adapt to the multiple consequences of global warming. The UN Climate Experts Group (Giec) is due to report in October on a possible planet at + 1.5 ° C. The draft text already estimated in January 2018 that in view of current country commitments and CO2 emission trajectories, it was " extremely unlikely " to achieve this goal.

The sea level will continue to rise " for at least three centuries "

Even if the temperature rise stabilizes at +1.5 or + 2 ° C, the sea level will continue to rise " for at least three centuries ", from 90 or 120 cm by 2300, according to one 20 studies compiled by the researchers. This will result in flooding, erosion and salinization of groundwater. The more optimistic the scenario, the more the Pacific Islands, the Ganges Delta or the coastal cities will have time to build defenses or move populations. If nothing is done to limit CO2 emissions, the average rise in sea level, caused by ice melt and water dilation, will reach 72 cm by 2100. But this perspective is variable depending on the temperatures. It is thus estimated at 65 for the scenario at + 2 ° C, while it could reach 130 years if climate change is maintained at + 1.5 ° C. " The impacts for the 21st century are rather postponed than avoided, " note the researchers.

More difficult access to food

According to studies, rising temperatures will lead to greater food insecurity around the world. This will be the consequence of both floods and larger droughts. A warming of 2 ° C would make it more vulnerable to the shortage of countries like Bangladesh, Oman, Mauritania, Yemen and Niger. On the contrary, Mali, Burkina Faso and Sudan would see their situation improve slightly as they would suffer from less severe droughts. But this is an " exception ", according to Professor Richard Betts, who conducted one of 20 studies. In case of a warming of 1.5 ° C, " 76% of the countries studied would record a lower increase in their vulnerability to food insecurity, " the researchers report.

Poorer countries even poorer

While a temperature increase of + 1.5 ° C is not likely to change global economic growth much, " a warming of 2 ° C suggests significantly lower growth rates for many countries, especially around the world. 'equator ', says Felix Pretis, an economist at Oxford University. " The already poor countries today are expected to become even poorer with climate change, and more when temperatures rise by + 2 ° C than by + 1.5 ° C. Rich countries are likely to less affected, "says Felix Pretis.

A significant difference for biodiversity

If a rise in temperatures will disrupt some of the fauna and flora, " containing the warming at 1.5 ° C rather than 2 ° C (...) would increase from 5.5 to 14% areas of the globe that could serve as a climate refuge for plants and animals, "says another study. Their area would be equivalent to that of the " current network of protected areas ". In addition, limiting global warming could reduce by nearly 50% the number of species at risk of halving their natural habitat.

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