On May 28 we ran the fourth (GRN Volume 5, Issue 21) in a Global Renewable News series under the heading Summary for Policymakers whereby Working Group 1¹ to the Intergovernmental Panel on Climate Change (IPCC) looked at new evidence of climate change. This fifth essay is a continuation of the information used to explain findings that are having a very real effect on our planet and our lives.

Future Global and Regional Climate Change continued:

D.2 Atmosphere: Water Cycle

Changes in the global water cycle in response to the warming over the 21^st century will not be uniform. The contrast in precipitation between wet and dry regions and between wet and dry seasons will increase, although there may be regional exceptions.

• Projected changes in the water cycle over the next few decades show similar large-scale patterns to those towards the end of the century, but with smaller magnitude. Changes in the near term and at the regional scale will be strongly influenced by natural internal variability and may also be affected by anthropogenic aerosol emissions.
• The high latitudes and the equatorial Pacific Ocean will likely experience an increase in annual mean precipitation by the end of this century. A temperature increase is likely in many mid-latitude wet regions. Mid-latitude and subtropical dry regions will see a decrease in mean precipitation.
• By the end of the 21^st century, extreme precipitation events over most of the mid-latitude land masses and wet tropical regions will almost certainly become more intense and more frequent.
• Globally, the area encompassed by monsoon systems will definitely experience increases over the rest of this century and onset dates are likely to become earlier and storm season will last longer. While monsoon winds are likely to weaken, associated precipitation will intensify due to the increase in atmospheric moisture.
• Data shows that the El Niño-Southern Oscillation (ENSO) will remain the dominant mode of interannual variability in the tropical Pacific with global effects. Due to the increase in moisture availability, ENSO-related precipitation variability on regional scales will intensify.

D.3 Atmosphere: Air Quality

• The range in projections of air quality (fine particulate matter [PM2.5] and ozone [O3] in near-surface air) is driven ostensibly by emissions (including methane [GH4]), rather than by physical climate change. Globally, warming decreases background surface ozone. High methane levels can offset this decrease raising background surface ozone by 2100 on average by about 8 parts per billion (ppb), which is 25 percent of current levels.
• Direct observation and modelling indicates that locally higher surface temperatures in polluted regions will trigger regional feedbacks in chemistry and local emissions that will increase peak levels of ozone and PM2.5. ForPM2.5, climate change may alter natural aerosol sources as well as removal by precipitation.

D.4 Ocean

The global ocean will continue to warm during the 21^st century. Heat will penetrate from the surface to the Deep Ocean and effect ocean circulation.

• The strongest ocean warming is projected for the surface in tropical and Northern Hemisphere subtropical regions. At greater depth the warming will be most profound in the Southern Ocean. Best estimates of warming in the top one hundred metres (328 feet) range from about 0.6 degrees Celsius [C] (1.1 degrees Fahrenheit [F]) to 2.0 degrees C (3.6 degrees F), and approximately 0.3 degrees C (0.5 degrees F) to 0.6 degrees C (1.1 degrees F) at a depth of some 1000 metres (3280 feet) by the end of this century.
• Atlantic Meridional Overturning Circulation (AMOC)* will weaken over the 21^st century. Estimates and ranges for the reduction are 11 percent (1% to 24%) and 34 percent (12% to 54%). It is likely there will be some decline as soon as 2050. Large natural internal variability may slow the decline in some years but overall, the prospects are alarming. Any slowdown in the overturning circulation would have profound implications for climate change.
• It is, however, highly unlikely that the AMOC will suffer an abrupt transition or collapse in this century. This ambiguity is purely due to limited analyses and equivocal results, not because we are treating Mother Nature with any more respect.

D.5 Cryosphere

It is very likely the Arctic sea ice will continue to shrink and thin. Northern Hemisphere spring snow cover will decrease during the 21st century as global mean surface temperature rises. Global glacier volume will further shrink.

• Based on multi-model averages, year-round reductions in Arctic sea ice extent are projected by the end of this century. Reduction data during September range from 43 percent to 94 percent and from eight percent to 34 percent in February.
• Models most closely reproducing the climatological mean state and 1979 to 2012 trend of the Arctic sea ice extent see a nearly ice-free Arctic Ocean in September before mid-century.
• In the Antarctic, a decrease in sea ice extent and volume is projected, with some reservations, for the end of the 21^st century as global mean surface temperature rises.
• By the turn of the next century, the global glacier volume, excluding glaciers on the periphery of Antarctica, is projected to decrease anywhere from 15 percent to 55 percent.
• Northern Hemisphere spring snow cover is predicted to decrease anywhere from seven percent to 25 percent by the end of this century.
• It is certain that near-surface permafrost extent at high northern latitudes will be reduced as global mean surface temperature increases. As this century closes out, the area of permafrost near the surface (upper 3.5 metres/11.5 feet) is projected to decrease by between 37 percent and 81 percent for the model average.

As I keep saying:

It’s time to shelve the hubris and try to understand the ramifications of these on-going changes. We need to use our combined intelligence to learn from these findings and save this planet – the very one and only that has given us the life that we enjoy but are definitely taking advantage of.
 

*The AMOC carries warm upper waters longitudinally into far-northern latitudes to be cooled and returns cold deep water southward across the Equator. This hot/cold equilibrium makes a substantial contribution to maintaining the moderate climate of maritime and continental Europe as well as the east coast of North America.

¹ IPCC, 2013: Summary for Policymakers. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group 1 to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.