I recently completed the third in a Global Renewable News series under the heading 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 16 – April 22 [Earth Day]). This fourth essay is a continuation of the information used to explain findings that are having a very real effect on our planet and our lives.

Understanding the Climate System and its Recent Changes continued

C.3. Detection and Attribution of Climate Change
Combined observations, studies of feedback processes, and model simulations offer up the best results when understanding recent changes in our climate system. This requires consideration of the state of all modelled climate system components at the beginning of a session along with the natural and anthropogenic factors used to drive the models. Working in our favour is the fact that longer and more detailed observations plus improved climate models now enable the attribution of human forcing to detected changes in more of the components.

Human influence has been detected in warming of the atmosphere and the ocean, in changes in the global water cycle, in reductions in snow and ice, in global mean sea level rise, and in changes in some climate extremes.* Strong evidence indicates that more than half of the increase (0.5 to 1.3 degrees Celsius [C]/0.9 to 2.3 degrees Fahrenheit [F]) from 1951 to 2010 was caused by the anthropogenic increase in greenhouse gases (GHGs). This includes the cooling effect of aerosols (-0.6 to 0.1 degrees C/-0.7 to 0.18).

• Over every continental region except Antarctica, humans have been complicit in surface temperature increases, particularly since mid-20th century. For Antarctica, it is more difficult to determine to what level anthropogenic forcings have contributed to the warming averaged due to fewer available observation stations.
• Anthropogenic influence, mainly GHGs and stratospheric (layer immediately above the troposphere sits 10 to 13 kilometres above Earth’s surface) ozone depletion has led to a detectable observed pattern of tropospheric (lowest layer of Earth's atmosphere averaging 11 kilometres in depth at mid-latitudes) warming and a corresponding cooling in the lower stratosphere since 1961.
• Global upper ocean (0 to 700 metres) heat content has increased significantly since the 1970s.
• Since 1960, big data is showing that the global water cycle is being affected. Observed increases are well documented in atmospheric moisture content, global-scale changes in precipitation patterns over land, intensification of extreme precipitation to make landfall, and changes in surface and sub-surface ocean salinity.
• Human influence has contributed to observed global scale changes in the frequency and intensity of daily temperature extremes since mid-20th century. The probability of heat waves in some locations has more than doubled.
• Arctic sea ice loss since 1979 is one of the worst calamities attributable to human influence and interference. Retreating glacial ice has increased dramatically since the 1960s and the Greenland ice sheet has been dwindling steadily since 1993.**
• There are observed reductions in Northern Hemisphere spring snow cover since 1970.
• Global mean sea level rise since the 1970s can be attributed to anthropogenic influence. The two largest contributors to the rise are thermal expansion and loss of glacier mass.
• Based on direct satellite measurements total solar irradiance has not contributed to global mean surface temperature over the period 1986 to 2008. Some experts feel that the 11-year cycle of solar variability influences decadal climate fluctuations in some regions. In addition, little association between changes in cosmic rays and cloudiness has been identified.

D. Future Global and Regional Climate Change
Projections of changes in the climate system are made using a selection of climate models including:

1. Basic
2. Intermediate complexity
3. Fully comprehensive
4. Earth System

They work by simulating changes based on a set of scenarios of anthropogenic forcings. A new set of scenarios, the Representative Concentration Pathways (RCPs) was used for the new climate model simulations carried out under the framework of the Coupled Model Intercomparison Project Phase 5 (CMIP5) of the World Climate Research Programme. In all RCPs, atmospheric CO2 concentrations are higher in 2100 relative to present day as a result of a further increase of cumulative emissions of CO2 to the atmosphere during the 21^st Century. Projections in this summary for policymakers are for the end of the 21^st century (2081 to 2100) given relative to 1986 to 2005.¹

Continued emissions of GHGs will cause further warming and changes in all components of the climate system. Limiting climate change will require substantial and sustained reductions of GHG emissions.

• Projections for the next few decades show spatial patterns of climate change similar to those projected for the latter 21^st century but with smaller impacts. To be sure, natural internal variability will continue to be a major influence on climate, particularly in the near-term and at the regional scale. By mid-century, however, science shows the magnitudes of the projected changes are substantially greater as a result of more GHGs being released.
• Improved modelling and data acquisition around land-ice contributions are showing much higher rises in sea level than previously projected.

D.1 Atmosphere: Temperature
Global surface temperature change by the end of this century is likely to exceed 1.5 degrees C (2.7 degrees F) relative to 1850 to 1900. Under all scenarios, warming will continue beyond 2100 and continue to exhibit interannual-to-decadal variability and will not be uniform region by region.

• Global mean temperature for 2016 to 2035 relative to 1986 to 2005 will likely be in the range of 0.3 to 0.7 degrees C (0.5 to 1.3 degrees F). Major volcanic eruptions and secular changes in solar irradiance are not factored in. Due to relative natural internal variability, near-term increases in seasonal and annual mean temperatures are expected to be higher in the tropics and subtropics than in mid-latitudes.
• As evidenced by the nearly endless confused polar vortexes during the winter/spring of 2013/2014 the Arctic region is warming faster than the global mean. Warming over land is faster than that over the ocean.
• By the end of the 21^st century, warming is expected to come in anywhere between 1.5 to 2.0 degrees C (2.7 to 3.6 degrees F).

It is almost certain there will be more frequent hot and fewer cold temperature extremes over most land areas on daily and seasonal timescales as global mean temperature increases. Heat waves will definitely occur more frequently, with more voracity, and will be longer-lasting. Polar vortexes will continue to sink more southern areas into deep-freeze while the Arctic gets warmer.

In the next issue, I will continue to look at the atmosphere specifically; water cycles, air quality, oceans, cryosphere, sea level, carbon and other biochemical cycles, and climate stabilization, climate change commitment and irreversibility.

And I say again:

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.
 

*Annual global mean combined land and sea surface temperatures have steadily risen from -0.4 degrees C (-0.7 degrees F) in 1850 to 0.6 degrees C (1.1 degrees F) in 2012.
**The Antarctic and Greenland ice sheets contain approximately 99 percent of the Earth's fresh water.

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.