Why does 1.5C warming goal matter to global poverty and health?

BARCELONA - Limiting global warming to the lower target governments agreed to aim for in a 2015 accord could reduce the number of people exposed to climate risks and susceptible to falling into poverty by up to several hundred million by 2050, climate scientists said in a key United Nations report on Monday.

Under the Paris Agreement, almost 200 nations committed to keep the rise in global temperatures to "well below" 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial levels and to strive for a more ambitious goal of 1.5 degrees.

In a statement on the U.N. report, which was approved by governments at the weekend, the Intergovernmental Panel on Climate Change (IPCC) said limiting global warming to 1.5C would require "rapid, far-reaching and unprecedented changes" in all aspects of society, and bring "clear benefits to people and natural ecosystems".

Sticking to the lower ceiling could go hand in hand with ensuring a more sustainable and equitable society, it added.

Here are the some of the key differences in climate change impacts on people expected at 1.5C versus 2C of global warming, as outlined in the new assessment (degrees of confidence in outcomes vary between very high, high and medium):

* Climate-related risks to health, livelihoods, food security, water supply, human security and economic growth are projected to increase with global warming of 1.5C, and increase further with 2C.

* Those at disproportionately higher risk of the adverse consequences of global warming at 1.5C and beyond include disadvantaged and vulnerable populations, some indigenous peoples and local communities that make a living from agriculture or coastal activities like fishing.

* Regions that are particularly threatened include Arctic ecosystems, dry regions, small-island developing states and least-developed countries.

* Any increase in global warming is expected to affect human health, largely negatively. The risk of heat-related deaths is lower at 1.5C than at 2C, while risks from some insect-carried diseases, such as malaria and dengue fever, are likely to rise with the temperature.

* Limiting global warming to 1.5C compared to 2C could reduce the proportion of the world population exposed to increasing water stress by up to half, although this varies considerably between regions.

* Sticking to the 1.5C target would keep global sea level rise 0.1 metre (3.9 inches) lower by 2100 than warming of 2C. That suggests up to 10 million fewer people would be exposed to related risks, based on 2010 population levels and if no adaptation occurs.

* If sea levels rise more slowly, there will be greater opportunities for small islands, low-lying coastal areas and deltas to adjust to coastal flooding, saltwater intrusion and damage to infrastructure, among other risks.

* Countries in the tropics and Southern Hemisphere subtropics are projected to see the largest negative impacts on economic growth due to climate change if warming rises from 1.5C to 2C.

* Extreme hot days in the planet's mid-latitude temperate regions would be hotter by up to about 3C at global warming of 1.5C, and 4C at 2C of warming. Overall, the number of hot days is projected to increase in most regions, especially in the tropics.

* Risks from droughts and rainfall shortages are likely to be higher in some regions at 2C of global warming compared to 1.5C.

* Heavy rainfall associated with tropical cyclones is projected to be higher at 2C compared to 1.5C of global warming. Globally, heavy precipitation is likely to be higher at 2C of warming and, as a consequence, the fraction of the world's land affected by floods is also projected to be larger.

* Holding warming to 1.5C is projected to result in lower net declines in yields of maize, rice, wheat and potentially other cereal crops, particularly in sub-Saharan Africa, Southeast Asia, and Central and South America.

* Less food is likely to be available at 2C of warming than at 1.5C in the Sahel, southern Africa, the Mediterranean, central Europe and the Amazon. Livestock are also expected to be adversely affected as temperatures rise.

* Curbing warming to 1.5C rather than 2C would be less damaging for global efforts to develop in a sustainable way, eradicate poverty and reduce inequality.

Source: Summary for Policymakers of the IPCC Special Report on Global Warming of 1.5ºC - http://report.ipcc.ch/sr15/pdf/sr15_spm_final.pdf