Climate Change: Why aren't more people concerned about it?

Currently as N Division leader (a position he holds since 2002) he oversees the basic and
applied research activities in Nuclear Physics, Particle Physics and Accelerator
Technologies. An important aspect of this activity is to seek alignment between the basic
research goals of the division and the goals of LLNL’s programs in nuclear weapons
stewardship, nonproliferation, homeland security and the National Ignition Facility.

DIRECT RISKS: The risks of climate change are non-linear: while average conditions may
change gradually, the risks can increase rapidly. On a high emissions pathway, the probability of
crossing thresholds beyond which the inconvenient may become intolerable will increase over
time.

• For any emissions pathway, a wide range of global temperature increases is possible. On all but
the lowest emissions pathways, a rise of more than 2°C is likely in the latter half of this century. On
a medium-high emissions pathway (RCP61), a rise of more than 4°C appears to be as likely as not by
2150. On the highest emissions pathway (RCP8.5), a rise of 7°C is a very low probability at the end of this century, but appears to become more likely than not during the course of the 22nd century. A rise of more than 10°C over the next few centuries cannot be ruled out.

• Humans have limited tolerance for heat stress. In the current climate, safe climatic conditions for
work are already exceeded frequently for short periods in hot countries, and heat waves already cause fatalities. In future, climatic conditions could exceed potentially lethal limits of heat stress even for individuals resting in the shade. The probability of exposed individuals experiencing such conditions in a given year starts to become significant for a global temperature rise of around 5°C, and could exceed 50% for a global temperature rise of around 7°C, in hot areas such as northern India, southeastern China, and southeastern USA.

• Crops have limited tolerance for high temperatures. When critical thresholds are exceeded, yields may be drastically reduced. The probability of crossing such thresholds in a given year, for studied examples of maize in the Midwestern US and rice in southern China, appears to rise from near zero at present, to become increasingly significant with global temperature rise of more than 2°C, and in the worst cases to reach somewhere in the region of 25% (maize) and 75% (rice) respectively with global temperature rise of around 4-5°C.Biophysical limits on the extent to which such tolerance thresholds can be raised may be an important constraint on adaptation. This is one reason why high degrees of climate change could pose very large risks to global food security.

• Thresholds for water stress are largely arbitrary, but thresholds of ‘moderate’, ‘chronic’ and ‘extreme’ water shortage are widely used, based on per capita availability. The number of people exposed to extreme water shortage is projected to double, globally, by mid century due to population growth alone. Climate change could increase the risk in some regions: for example, on a high emissions pathway, the probability of the Tigris – Euphrates river basin falling into extreme water shortage could rise significantly after 2030, reaching close to 100% by 2070.

• In South and East Asia, climate change may slightly offset otherwise increasing risks of water stress, while increasing the risk of flooding. On a high emissions pathway, what is now a ‘30-year flood’ could become three times more frequent in the Yellow River and Indus basins, and six times more frequent in the Ganges basin, over the course of the century, on a central estimate. In the worst case for those three river basins, such a flood could be in the region of ten times more frequent by the end of the century.

• On a high emissions pathway, the incidence of extreme drought affecting cropland could increase by about 50% in the US and South Asia, double globally, and triple in southern Africa, over the course of the century under central estimates. The uncertainties around these central estimates are large: for the US and South Asia, in the best case, drought incidence could halve; in the worst case, it could increase by three or four times.

• With 1m of global sea level rise, the probability of what is now a ‘100-year flood event’ becomes
about 40 times more likely in Shanghai, 200 times more likely in New York, and 1000 times more likely in Kolkata. Defences can be upgraded to maintain the probability of a flood at a constant level, but this will be expensive, and the losses from flooding will still increase, as the floods that do occur will have greater depth. Thresholds of adaptation beyond which ‘retreat’ from the sea may become more feasible than further increases in flood protection are not well defined, but the most significant limits may be sociopolitical rather than economic or technological.

• Climate models suggest that global sea level rise is unlikely to exceed 1m this century, and that a
plausible worst-case scenario could result in an increase of several metres by the end of the 22nd
century. However, due to inertia in the climate system, with a sustained global temperature rise of 2°C the global sea level may be committed to rise by some 10-15m as ice-sheets gradually melt, but whether this will take hundreds of years or thousands of years is deeply uncertain.

• Many elements of the climate system are capable of abrupt or irreversible change. Changes to
monsoons or to ocean circulation patterns, die-back of tropical forests, and the release of carbon
from permafrost or sub-sea methane hydrates could all cause large-scale disruption of the climate.
The probabilities of such changes are not well known, but they are expected to increase as the global temperature rises.