Thursday, November 22, 2012

Impact of a 4 degree hotter world

In its new report (Turn Down the Heat: Why a 4°C Warmer World Must be Avoided), the World Bank has warned of “a cascade of cataclysmic changes that include extreme heat-waves, declining global food stocks and a sea-level rise affecting hundreds of millions of people” if the global community fails to act on climate change, which might heat up Earth by 4 degree Celsius (4°C)— above pre-industrial levels—by end of this century. It says that the current greenhouse gas emissions pledges are insufficient to bring down projected temperature rise.

An interesting part of such studies is the key findings, which seeps into the policy document of development agencies, I/NGOs and governments. Anyway, here are some of the key findings:
  • Global temperature is now 0.8°C above preindustrial levels. It could cross 4°C by the end of the century in the absence of collective efforts by global community.
  • Extreme heat waves will be experienced during almost all summer months in many regions. Increase of 6°C or more would be expected in the Mediterranean, North Africa, Middle East and parts of the US.
  • Likely rise in sea level by 0.5 to 1 meter by 2100. Many small islands may not be able to sustain their populations.
  • Most vulnerable regions are in the tropics, sub-tropics and towards the poles.
  • Agriculture, water resources, human health, biodiversity and ecosystem services are likely to be severely impacted.
  • CO2 concentration has increased from 278 ppm in preindustrial time to 391 ppm in September 2012 with rate of rise now at 1.8 ppm per year.
  • Emissions of CO2 are at 35000 million metric tons per year and projected to rise to 41000 million metric tons per year in 2020.
  • Over the last decade the average rate of sea-level rise has increased to about 3.2 cm per decade. With this rate, it could be over 30 cm of additional sea-level rise in the 21st century. Limiting temperature to 2°C would likely reduce sea-level rise by about 20 cm by 2100 compared to a 4°C world.
  • Record minimum Arctic sea ice in September 2012, halving the area of ice covering the Arctic Ocean in summers over the last 30 years.
  • The heat wave of 2010 in Russia claimed 55000 lives. It also resulted in 25% crop failure, burned areas at more than 1 million hectares and cost US$15 billion. With 4°C rise in mean temperature, such heat waves are likely to be a normal feature.
  • The 202 drought in the US impacted about 80% of agricultural land, making it the most severe drought since the 1950s.
  • Substantial increases in stunting due to malnutrition are projected to occur with warming of 2°C to 2.5°C, especially in Sub-Saharan Africa and South Asia, and this is likely to get worse at 4°C.
Earlier, there were studies that looked at the impact of climate change on growth and trade. By analyzing the historical fluctuation in temperature in 125 countries between 1950 and 2003, Dell, Jones and Olken (ungated version here) found that it does not have significant economic impact in rich countries, but in poor countries one standard deviation increase in mean annual temperature reduces economic growth by 0.69 percentage points. It impacts agriculture and industrial outputs, political stability, and leadership transitions.  In a research note, Canuto and Onder discuss three ways through with trade intensity affects emissions.
  1. Increased trade means increased production, which means increased emissions—scale effect
  2. Greater specialization on production and export of goods might lower or increase emissions depending on the production structure, i.e. if it is polluting or non-polluting economic activity (think of coal and hydroelectricity respectively)— composition effect
  3. Technology transfer might promote ‘cleaner’ ways to produce goods— technique effect
Additionally, a recent analysis of land-surface temperature by Berkeley Earth shows that the rise in average world land temperature is approximately 1.5°C in the past 250 years, and about 0.9°C in the past 50 years. Importantly, it shows that humans are responsible for the increase in temperature especially in the last 50 years.