On June 3 (GRN Volume 5, Issue 22), we ran the fifth installment in a Global Renewable News series under the heading Summary for Policymakers. In it Working Group 1 to the Intergovernmental Panel on Climate Change (IPCC)¹ looked at new evidence of climate change. This final 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.6 Sea Level

Global mean sea level will continue to rise during this century. The rate of rise will exceed that observed during 1971 to 2010 due to increased ocean warming and shrinking mass from glaciers and ice sheets.

• Understanding the likelihood of global mean sea level rise has gotten better due to:
  
  1. Better physical understanding of the components of sea level
  2. Improved agreement of process-based models and observations
  3. The inclusion of ice-sheet dynamical range
• Sea level rise across the globe for 2008 to 2100 relative to 1986 to 2005 will likely be in the ranges of 0.26 metres to 0.55 metres (10.2” to 21.7”) and 0.33 metres to 0.63 metres (13” to 24.8”) depending on the type of model used to extrapolate data. The highest rise will occur during 2081 to 2100 with an anticipated rise of 8mm to 16mm (5/16” to 5/8”) per year. These figures are arrived at with the aid of process-based models and literature assessment of glacier and ice sheet contributions.
• Thermal expansion accounts for 30 percent to 55 percent of 21^st century global mean sea level rise and glaciers for 15 percent to 35 percent. The increase in surface melting of the Greenland ice sheet will increase in snowfall, leading to a positive contribution from changes in surface mass balance to future sea level. Numbers are showing that while surface melting will remain small, an increase in snowfall on the Antarctic ice sheet is expected, resulting in a negative contribution to future sea level changes in surface mass balance. Changes in outflow from both ice sheets combined will likely make a contribution in the range of 0.03 meters to 0.2 metres (1.2” to 7.9”) by 2081 to 2100.
• Based on current understanding, only the collapse of marine-based sectors of the Antarctic ice mass could cause global mean sea level rise substantially above any likely range during this century. However, this additional contribution would not exceed several tenths of a meter of rise.
• Sea level rise will not be uniform. By the end of the 21^st century, it is deemed likely that levels will rise in more than 95 percent of the ocean area. Approximately 70 percent of coastlines worldwide are projected to experience sea level change within 20 percent of the global mean sea level change.

D.7 Carbon and Other Biogeochemical Cycles

Climate change will affect carbon cycle processes in a way that will exacerbate the increase of CO₂ in the atmosphere. Further uptake of carbon by the ocean will increase ocean acidification.

• Ocean uptake of anthropogenic CO₂ will continue through 2100. The future evolution of the land carbon uptake is less certain. A majority of models project a continued land carbon uptake across all scenarios with some models simulating a land carbon loss due to the combined effect of climate change and land use change.
• Based on Earth System Models (ESMs), the feedback between climate and the carbon cycle is positive in this century; that is, climate change will partially offset increases in land and ocean carbon sinks caused by rising atmospheric CO₂. As a result more of the emitted anthropogenic CO₂ will remain in the atmosphere. A positive feedback between climate and the carbon cycle on century to millennial time scales is supported by paleoclimate observations and modelling.
• Taking into account all possible outcomes, projections by ESMs show a global increase in ocean acidification.
• The release of CO₂ or CH₄ to the atmosphere from thawing permafrost carbon stocks over the 21^st century is assessed to be in the range of 50 to 250 Gigatonnes of carbon (GtC).

D.8 Climate Stabilization, Climate Change Commitment, and Irreversibility

Cumulative emissions of CO₂ will largely determine global mean surface warming by the late 21^st century and beyond. Most aspects of climate change will persist for many centuries even if emissions of CO₂ are stopped. This represents a substantial multi-century climate change commitment created by past, present, and future emission of the gas.

• Cumulative total emissions of CO₂ and global mean surface temperature are approximately linearly related. Any given level of warming is associated with a range of cumulative CO₂ emissions. This means, for example, that higher emissions in earlier decades imply lower emissions later.
• Accounting for warming effects of increases in non-CO₂ GHGs, reductions in aerosols, or the release of GHGs from permafrost will lower the cumulative CO₂ emissions for a specific warming target.
• A large fraction of anthropogenic climate change resulting from CO₂ emissions is irreversible on a multi-century to millennial time scale, except in the case of a large net removal of CO₂ from the atmosphere over a sustained period. Surface temperatures will remain approximately constant at elevated levels for many centuries after a total cessation of net anthropogenic CO₂ emissions. Due to the long time scales of heat transfer from the ocean surface to depth, ocean warming will continue for centuries. Science claims that about 15 percent to 40 percent of emitted CO₂ will remain in the atmosphere for more than 1000 years.
• It is virtually certain that global mean sea level rise will continue beyond 2100, with rise due to thermal expansion to continue for many centuries. Models show that beyond 2100 sea level rise above the pre-industrial level by 2300 to be less than one metre (3.28 feet) for a radiative forcing that corresponds to CO₂ concentrations that peak and decline and remain below 500 ppm.
• Sustained mass loss by ice sheets would cause greater sea level rise, and some part of the mass loss might be irreversible. Sustained warming would lead to the near-complete loss of the Greenland ice sheet over a millennium or more, causing a global mean sea level rise of up to seven metres (23 feet). Current estimates indicate that the threshold could be approximately 4 degrees C (7.2 degrees F) global mean warming with respect to pre-industrial. Abrupt and irreversible ice loss from a potential instability of marine-based factors of the Antarctic ice sheet in response to climate forcing is possible.
• Methods that aim to deliberately alter the climate system to counter climate change, termed geoengineering, have been proposed. Limited evidence precludes a comprehensive quantitative assessment of both Solar Radiation Management (SRM) and Carbon Dioxide Removal (CDR) and their impact on the climate system. CDR methods have biogeochemical and technological limitations to their potential on a global scale. There is insufficient knowledge to quantify how much CO₂ emissions could be partially offset by CDR on a century timescale. Modelling indicates that SRM methods, if realizable, have the potential to substantially offset a global temperature rise, but they would also modify the global water cycle, and would fail to reduce ocean acidification. If SRM were terminated for any reason, global surface temperatures would rise very rapidly to values consistent with GHG forcing. CDR and SRM methods carry side effects and long-term consequences on this planet that we call home.

For the last time I say:

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.
 

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.