In a recent Global Renewable News, I discussed the document entitled Summary for Policymakers whereby Working Group 1 to the Intergovernmental Panel on Climate Change (IPCC) looked at new evidence of climate change (see GRN Volume 5, Issue 11 – March 19). In this essay, I continue to explain findings that are having a very real effect on our planet and our lives.

A.4 Sea Level
The rate of sea level rise since the mid eighteen hundreds has been greater than the mean rate during the previous two millennia. In fact, from 1901 to 2010, global sea level rose by 0.19 (0.17 to 0.21) metres.¹

• According to instrumental sea level data, a transition took place in the late 19^th to the early 20^th century from relatively low mean rates of rise over the previous two millennia to higher rates of rise. The rate of global mean sea level rise has continued to increase since the early 20^th century.
   
• The yearly global sea level rise (millimetres per year) was: Tide-gauge and satellite altimeter data are consistent regarding the higher rate of the latter period. It appears that similarly high rates occurred between 1920 and 1950.
  
  • 1901 to 2010 – 1.7 (1.5 to 1.9)
  • 1971 to 2010 – 2.0 (1.7 to 2.3)
  • 1993 to 2010 – 3.2 (2.8 to 3.6)
     
• Since the early 1970s glacier mass loss and ocean thermal expansion due to warming together show about 75 percent of the observed global mean sea level rise. Global mean sea level rise over the period 1993 to 2010 is consistent with the sum of observed conditions from ocean thermal expansion due to warming (shown in millimetres per year):
  • Glaciers – 0.76 [0.39 to 0.38]
  • Greenland ice sheet – 0.33 [0.25 to 0.41]
  • Antarctic ice sheet – 0.27 [0.16 to 0.38]
  • Land water storage – 0.38 [0.26 to 0.49]
  The sum total of these contributions is 2.8 [2.3 to 3.4] millimetres per year
   
• Maximum global mean sea level during the last interglacial period (129,000 to 116,000 years ago) was, for several thousand years, at least five metres higher than present but did not exceed 10 metres above present. During this interglacial period, the Greenland ice sheet contributed between 1.4 and 4.3 metres to the higher global mean sea level. Based on this it seems assured that the Antarctic ice sheet also contributed to the overall rise. Data extrapolated from several thousand years shows that high-latitude surface temperature averaged at least two degrees Celsius warmer than present.
   

A.5 Carbon and Other Biogeochemical Cycles
The atmospheric concentrations of carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) have increased to levels unprecedented in at least the last 800,000 years. Carbon dioxide concentrations have increased by 40 percent since pre-industrial times, primarily from fossil fuel emissions and secondarily from net land use change emissions. The ocean has absorbed about 30 percent of the emitted anthropogenic CO₂, causing ocean acidification.²

• The atmospheric concentrations of the greenhouse gases (GHGs) CO₂, CH₄ and N₂O have all increased since 1750 due to human activity. In 2011, the concentrations of these GHGs exceeded pre-industrial levels by some 40 percent.
   
• Concentrations of GHGs now substantially exceed the highest concentrations recorded in ice cores during the past 800,000 years. The mean rates of increase in atmospheric concentrations over the past century are unprecedented in the last 22,000 years.
   

B. Drivers of Climate Change
All natural and anthropogenic substances and processes that alter the earth’s energy budget are drivers of climate change. A term known as Radiative Forcing (RF) quantifies the change in energy flow caused by driver changes dating from 2011 back to 1750. Positive RF leads to surface warming and negative RF means surfaces are cooling. Data is taken from a variety of sources including: in-situ; remote; properties of GHGs and aerosols; and calculations using numerical models representing observed processes. The RF can be based on the concentration changes of each substance. Alternatively, the emission-based RF of a compound can provide a more direct link to actual human activities and takes into account contributions from all substances affected by that emission. The total anthropogenic RF of the two approaches is identical when considering all drivers.

Total RF is positive. This has led to an uptake of energy by the climate system. The largest contribution of total radiative forcing is caused by the increase in the atmospheric concentration of CO₂ since 1750.³

• Total anthropogenic RF for 2011 relative to 1750 is 2.29 [1.13 to 3.33] watts per square metre (W/m²). This has increased far more rapidly since 1970 than during prior decades. The total anthropogenic RF best estimate for 2011 is 43 percent higher than that reported 2005 Assessment Report (AR4). This is caused by a combination of continued growth in most greenhouse gas concentrations and improved estimates of RF by aerosols indicating a weaker net cooling effect (negative RF).
   
• Emissions of CO₂ alone have caused an RF of 1.68 [1.33 to 2.03] W/m². Inclusion of other carbon-containing gases continues to increase the level of CO₂ concentrations.
   
• Emissions of CH₄ alone have caused a much larger RF than the concentration-based estimate. This difference in estimates is caused by concentration changes in ozone and stratospheric water vapour due to CH₄ and other emissions indirectly affecting CH₄.
   
• Emissions of stratospheric ozone-depleting halocarbons have caused a net positive RF. Their own positive RF has outweighed the negative RF from the ozone depletion they have induced. The positive RF from all halocarbons (i.e., fluorine, chlorine, bromine, iodine) is similar to the value in AR4, with a reduced RF from Chlorofluorocarbons (CFCs) but increases have been documented from many of their substitutes.
   
• The total anthropogenic RF continues to rise due to emissions of short-lived gases. Emissions of carbon monoxide (CO) are virtually certain to have induced a positive RF, while emissions of nitrogen oxides (NO_x) are likely to have induced a net negative RF.
   
• The RF of the total aerosol effect in the atmosphere, which includes cloud adjustments due to aerosols, is –0.9 [–1.9 to −0.1] W/m², and results from a negative forcing from most aerosols and a positive contribution from black carbon absorption of solar radiation. Studies show that aerosols and their interactions with clouds have offset a substantial portion of global mean forcing from well-mixed GHGs. They continue to contribute the largest uncertainty to the total RF estimate.
   
• The forcing from stratospheric volcanic aerosols can also have a large impact on the climate for several years after eruptions. The RF value for the years 2008 to 2011, for example, had twice the impact than during the years 1999 to 2002.
   
• Satellite observations of total solar irradiance changes from 1978 to 2011 indicate that the last solar minimum was lower than the previous two (2008 and 1986 minimums). Total natural RF from solar irradiance changes and stratospheric volcanic aerosols made only a tiny contribution to the net RF throughout the last century.

In future issues I will look at understanding the climate system changes and evaluate climate models.

I have already stated that warming of the climate system is unequivocal. Since the 1950s, many of the observed changes were unprecedented over decades to millennia. Concentrations of greenhouse gases such as CO₂, CH₄, halocarbons, N₂O, CO, NMVOC, NO_x, aerosols and precursors (mineral dust, sulphur dioxide, ammonia, organic carbon and black carbon) continue to play hell with life.

It’s time for us to understand, as fully as we can the ramifications of these on-going changes and use this information to save this planet that has given us the very life that we are taking advantage of.
 

¹ Stocker, T.F. et al. IPCC, 2013: “Summary for Policymakers.” Climate Change 2013: the Physical Science Basis. Contribution of Working Group 1 to the Fifth Assessment Report (AR5) of the IPCC.
² Ibid.
³ Ibid.