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Summary of Climate Change
An Introduction

by
Al Crawford


Global anthropogenic greenhouse gas (GHG) emissions
Global anthropogenic GHG emissions
a) Global annual emissions of anthropogenic GHGs from 1970 to 2004 (b) Share of different anthropogenic GHGs in total emissions in 2004 in terms of carbon dioxide equivalents (CO2-eq). (c) Share of different sectors in total anthropogenic GHG emissions in 2004 in terms of CO2-eq. (Forestry includes deforestation.)

During the year 2007 the Intergovernmental Panel on Climate Change (IPCC) issued its Fourth Assessment Report (AR4) which consisted of a series of four parts ending with the AR4 Synthesis Report which was released on November 17, 2007.  There is a consensus among climate scientists that this report represents either the "most reliable" or one of the most reliable sources for accurate information on climate change.

According to the IPCC the current climate changes that are occurring are mainly attributable to man-made emissions of greenhouse gasses (GHGs).  The table above (Figure 1) indicates the increasing amounts of anthropogenic (produced by human activities) GHGs that has occurred from 1970 through 2004.  Since 2004 the anthropogenic GHGs has been increasing at a rate of above 3% per year.  At this rate in 2010 the amount of carbon dioxide equivalents (CO2-eq) would be about 58.5 GtCO2-eq and in 2020 it would be 79 GtCO2-eq.  It is for this reason that the scientific community feels a great urgency to reduce, and reduce drasticly, the amounts of anthropogenic GHGs.

At this time the CO2 concentrations (see figure 3) in the atmosphere is abut 387 ppm.  That is compared with the range of CO2 concentrations the past 650,000 years when it ranged from 180 ppm to 300 ppm with an average of about 280 ppm (See figure 2).  This concentration is currently increasing at a rate of slightly more than 2 ppm/yr.  Most climatoligsts feel that it will be necessary to keep the CO2 concentrations to less than 560 ppm, which is twice the preindustrial value of 280 ppm.  At the current rate of increase it would reach that level in less than 90 years.  But this is assuming that GHG emissions will not increase.  And since emissions are increasing at a rate greater than 3% per year unless mankind takes some kind of action 560 ppm will be reached much before 90 years from now.  And iit is not known at what levels of warming will trigger natural releases of CO2 into the atmosphere which would cause even greater levels of warming.  (This triggering is referred to as a feedback loop.)


Temperature change (blue) and carbon dioxide change (red) observed in ice core records Many other records are available.


Figure 2
Figure 3


The point of the discussion GHGs is that they cause a warming of the earth.  Most of the GHGs occur naturally.  Without any GHGs the temperature of the atmosphere would be about -20 degrees  plunging the earth into a very deep freeze with all the oceans frozen.  The past few hundred years the GHGs have been relatively stable and the earth's temperature has been relatively stable.  But the anthropogenic GHGs are upsetting that balance and causing the earth to heat up.   And that warming effects the climate, the amount of ice at mountain tops and in the polar regions, and the sea level.  And all of that will have, if GHGs continue to rise unabated, some pretty unpleasant consequences for mankind.  

Since the beginning of the industrial age the temperatures of the earth has been rising.  And this warming has accelerated strongly since 1975 (see figure 4.)  So far this warming is about 0.75oC.  While this seems to be a very small amount, it has already had some measurable effects on the earth's climate.  Since the polar regions are warming at a faster rate than the rest of the earth the ice in those regions are melting.  This is particularly true of the arctic where the year 2007 saw a 23% decrease in the minimum ice cover than had been seen before.  And there has been wide spread retreating of glaciers world wide.  And patterns of drought and decreased snow cover is thought by some to be related to global warming.  The IPCC also predicts some catastrophic events due to warming if the worst case scenarios of 6oC or more warming occurs.  This would include an increase in sea levels that would endanger coastal areas, changes in climate that would change the areas where crops could be grown, turning some areas into desert regions, and the drying up of the Amazon basin.

The big question that some still ask are could the current warming trends be from natural causes.  And, according to virtually all climate scientists, the answer is a resounding "no".  There are a large number of effects that do cause  natural fluctuations in the climate system.  These include a number of regional cycles of ocean currents and temperatures (e.g. El Nino), the 11 year sunspot cycle, volcanoes, and other effects.  These will be discussed later.  But these known natural events cannot explain the current warming of the earth (see figure 5).  However, if the anthropogenic GHGs are factored in the current warming trend can be explained with the current models (see figure 6).


Figure 4


Figure 5

Figure 6

Current events that are or may be a result of the global warming that has already taken place.
What are the possible consequences of global warming.
What can be done to prevent the worst of the consequences.
Is it too late?