The US House of Representatives Committee on Science and Technology held a hearing on global warming last Thursday following the release of the IPCC (Intergovernmental Panel on Climate Change) Report a few days earlier. While there was recognition of the seriousness of the situation by many representatives, a few remained skeptical. Comments were made about the impact of dinosaurial and bovine flatulence on increase in methane levels. Despite the production of hot air it is not yet evident what actual actions will be produced as a consequence of the hearing.
Meanwhile let’s have a look at some other pieces of the IPCC summary report. I’ll show a couple of figures from the report, and a set of scenarios concerning emission of greenhouse gases. I’ll also present a (modified) table from the report that lists some of the consequences of warming.
Lest there be any doubt that the earth is being affected by climate change, Figure SPM-3 below shows actual changes that have occurred over the last 150 years in global mean temperature, global average sea level, and northern hemisphere snow cover.
FIGURE SPM-3. Observed changes in (a) global average surface temperature; (b) global average sea level rise from tide gauge (blue) and satellite (red) data and (c) Northern Hemisphere snow cover for March-April. All changes are relative to corresponding averages for the period 1961-1990. Smoothed curves represent decadal averaged values while circles show yearly values. The shaded areas are the uncertainty intervals estimated from a comprehensive analysis of known uncertainties (a and b) and from the time series (c).
Scientists have constructed several scenarios about how various changes in the economy and lifestyle will affect emissions of greenhouse gases. They then project how much warming will occur for each of these scenarios. The scenarios are given below and are followed by Figure SPM-7 which shows the associated warming trends.
The Emission Scenarios of the IPCC Special Report on Emission Scenarios (SRES)18
A1. The A1 storyline and scenario family describes a future world of very rapid economic growth, global population that peaks in mid-century and declines thereafter, and the rapid introduction of new and more efficient technologies.
Major underlying themes are convergence among regions, capacity building and increased cultural and social interactions, with a substantial reduction in regional differences in per capita income. The A1 scenario family develops into three groups that describe alternative directions of technological change in the energy system. The three A1 groups are distinguished by their technological emphasis: fossil intensive (A1FI), non-fossil energy sources (A1T), or a balance across all sources (A1B) (where balanced is defined as not relying too heavily on one particular energy source, on the assumption that similar improvement rates apply to all energy supply and end use technologies).
A2. The A2 storyline and scenario family describes a very heterogeneous world. The underlying theme is self reliance and preservation of local identities. Fertility patterns across regions converge very slowly, which results in continuously increasing population. Economic development is primarily regionally oriented and per capita economic growth and technological change more fragmented and slower than other storylines.
B1. The B1 storyline and scenario family describes a convergent world with the same global population, that peaks in mid-century and declines thereafter, as in the A1 storyline, but with rapid change in economic structures toward a service and information economy, with reductions in material intensity and the introduction of clean and resource efficient technologies. The emphasis is on global solutions to economic, social and environmental sustainability, including improved equity, but without additional climate initiatives.
B2. The B2 storyline and scenario family describes a world in which the emphasis is on local solutions to economic, social and environmental sustainability. It is a world with continuously increasing global population, at a rate lower than A2, intermediate levels of economic development, and less rapid and more diverse technological change than in the B1 and A1 storylines. While the scenario is also oriented towards environmental protection and social equity, it focuses on local and regional levels.
An illustrative scenario was chosen for each of the six scenario groups A1B, A1FI, A1T, A2, B1 and B2. All should be considered equally sound.
The SRES scenarios do not include additional climate initiatives, which means that no scenarios are included that explicitly assume implementation of the United Nations Framework Convention on Climate Change or the emissions targets of the Kyoto Protocol.
18 Emission scenarios are not assessed in this Working Group One report of the IPCC. This box summarizing the SRES scenarios is taken from the TAR and has been subject to prior line by line approval by the Panel.
Figure SPM-7. Solid lines are multi-model global averages of surface warming (relative to 1980-99) for the scenarios A2, A1B and B1, shown as continuations of the 20th century simulations. Shading denotes the plus/minus one standard deviation range of individual model annual means. The number of AOGCMs (Atmosphere-Ocean General Circulation multi-Model) run for a given time period and scenario is indicated by the coloured numbers at the bottom part of the panel. The orange line is for the experiment where concentrations were held constant at year 2000 values. The gray bars at right indicate the best estimate (solid line within each bar) and the likely range assessed for the six SRES marker scenarios. The assessment of the best estimate and likely ranges in the gray bars includes the AOGCMs in the left part of the figure, as well as results from a hierarchy of independent models and observational constraints
Finally, here is a table from the IPCC report that shows what are likely to be the effects of rising global temperature. (I have deleted a couple of columns and removed some footnote references for clarity of presentation).
Table SPM-1. (Modified) Recent trends, assessment of human influence on the trend, and projections for extreme weather events for which there is an observed late 20th century trend.
|Phenomena and direction of trend
||Likelihood of future trends based on projections for 21st century using SRES scenarios
|Warmer and fewer cold days and nights over most land areas
|Warmer and more frequent hot days and nights over most land areas
|Warm spells / heat waves. Frequency increases over most land areas
|Heavy precipitation events. Frequency (or proportion of total rainfall from heavy falls) increases over most areas
|Area affected by droughts increases
|Intense tropical cyclone activity increases
|Increased incidence of extreme high sea level (excludes tsunamis)
There are people who don’t believe that human activity is a main cause of present global warming. They do not wish to take actions such as requiring reductions in greenhouse gas emissions because they are concerned that the economy will suffer.
Now here is something for skeptics and believers alike to think about. From the data shown above it is quite evident that global temperature is increasing. Let’s consider a few cases concerning that trend.
1) Assume certain human activities are a major cause of rising global temperature. By reducing or eliminating those activities the rise in global temperature will be slowed.
2) If human activities that drive an increase in global temperature are not reduced or if they are increased, it (global temperature) will continue to rise, perhaps at an accelerated pace.
Both of the above cases imply that there is at least the potential for humans to affect the rate of rise of global temperature. But consider the following case:
3) Human activity does not cause a rise in global temperature. This is the scariest case since it means that humans are basically helpless in the face of observed rising temperatures.
Make no mistake, average global temperature is going to continue to rise for a while. The IPCC Summary Report makes the following statements:
“For the next two decades a warming of about 0.2°C per decade is projected for a range of […] emission scenarios. Even if the concentrations of all greenhouse gases and aerosols had been kept constant at year 2000 levels, a further warming of about 0.1°C per decade would be expected.”
“Continued greenhouse gas emissions at or above current rates would cause further warming and induce many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century.”
“Anthropogenic warming and sea level rise would continue for centuries due to the timescales associated with climate processes and feedbacks, even if greenhouse gas concentrations were to be stabilized.”
Clearly the earth is warming up and changes are occurring in the weather, sea-levels, etc. Regardless of the actual causes of these climatic changes, the results are beginning to have (and will have increasing) social and economic impact. Some actions must be taken to mitigate the adverse nature of these impacts otherwise there will be much disruption and misery in society. So who is leading the charge on this front and what is to be done?