GLOBAL WARMING: A Review and Update on Climate Science

By Ed Dreby

What is global warming and how does it relate to climate and climate change?

Climate refers to the general weather conditions and seasonal patterns that prevail in a particular region or locale over an extended period of time on a human scale.

Climate everywhere is affected by small quantities of greenhouse gases in the atmosphere that trap some of the earth's heat which would otherwise escape into space. This is called the greenhouse effect. It has kept the earth about 60 degrees F warmer than it would otherwise be and makes life possible.

Climates change naturally on a geological time scale. These changes are due to alterations in the sun's intensity, the position of the earth in relation to it, and the shape and location of continents. They affect global temperature, greenhouse gas concentrations, and global and regional climate in complex ways. As climates gradually change, plant and animal species evolve to adapt to new conditions.

Global warming refers to the rapid increase in global temperature now occurring because human activities are increasing the atmospheric concentrations of greenhouse gases.

What do scientists know about global warming, its causes and effects?

Greenhouse gases

Carbon dioxide is the predominant greenhouse gas. Its concentration in the atmosphere began to increase very gradually in the 18th century due to deforestation, and increased more rapidly in the late 19th century and throughout the 20th century due to extracting and burning fossil fuels and to more rapid deforestation. It is now 378 parts per million, compared with 280 ppm. in 1750, and is currently increasing at about 2 ppm/year.

Other greenhouse gases exist in much smaller amounts. However, they absorb more of the sun's radiation than carbon dioxide and are also increasing more rapidly, so their impacts have become significant. Since 1850, methane has increased from .78 ppm to 1.76 ppm, and nitrous oxide from .0278 ppm to .0319 ppm. The main industrial sources of methane and nitrous oxide relate to fossil fuels, large scale agriculture, and the accumulation of organic wastes.

It is estimated that about 60% of the overall warming effect is from carbon dioxide produced by extrating and burning fossil fuels, 18% from carbon dioxide related to deforestation and land use, 14% from methane, and 8% from nitrous oxide. Synthetic industrial gases, virtually non-existent in 1950, now contribute about 1% of the overall warming effect, and they too are continuing to increase. The US, with about 5% of world population, produces over 22% of the annual carbon dioxide emissions resulting from human activity.

Temperatures and their effects

Since 1900, global temperature has increased about 0.7 C degree (1.3 F degree). Since records have been kept, the 16 warmest years have occurred since 1983. To date, 1998 has been the warmest. Since 1999, every year has been warmer than the previous year except for 2004, which was virtually identical to 2003, both of which were almost as warm as 1998.

Ocean temperatures, both on the surface and at great depths, are rising. Because water expands as it warms, global sea level has risen: about 7 inches during the 20th century, and a full inch from 1995 to 2004. Oceans are also becoming more acidic. The number of extreme weather events, droughts on the one hand, and intense storms and floods on the other, has increased, largely because warmer air causes more water to evaporate.

The distribution of vegetation and wildlife has begun to shift significantly, as have growing seasons for agriculture. The earth's ice cover at the poles and at high elevations is shrinking, and the arctic tundra is thawing. Outbreaks of dengue fever, malaria, encephalitis, and other diseases carried by insects in temperate regions have been linked to global warming. Epidemics of insect infestation and diseases related to climate change are occurring in northern and temperate forests.

Fact, Interpretation, and the IPCC

The concentrations of greenhouse gases are measured directly via the analysis of air samples. Changes in global temperature are determined by combining and interpreting many different kinds of direct and indirect measures, and are therefore more subject to errors of measurement.

Weather patterns are known to be highly variable from year to year and place to place. Distinguishing between natural variability, changes due to natural factors, and changes due to human activity necessitates interpretation and is therefore subject to dispute. The relationship between climate change and ecosystem change is even more indefinite. The changes can be measured, but the causal relationships among them, as in any highly complex system, are far from simple or certain.

In 1988, when governments first became alarmed about global warming, the UN and its member governments established the IPCC to advise them about the implications of climate change for public policy. The IPCC consists of between 2000 and 2500 climate scientists, ecologists, and economists named by their governments. Its purpose is to periodically produce a consensus assessment of all the research findings relating to climate change and its effects. IPPC Assessments have been published in 1990, 1995, and 2001. The next is scheduled for 2007.

The IPCC's 2001 Assessment concluded that evidence gathered since the 1995 Assessment confirmed their previous findings, and convincingly linked human activity to higher land and ocean temperatures, rising sea levels, increased precipitation and storm intensities, thinning of snow and ice cover, and eco-system changes. Natural factors are possible contributors to all these changes as well, but accumulating evidence pointed more strongly toward human factors. This evidence also strengthened the IPCC's confidence in the ability of computerized climate modeling to anticipate future trends.

Recent findings

Since the 2001 Assessment, there has been more evidence of ocean warming, increased acidity, and changing circulation patterns; of melting glaciers and of thawing tundra, all of which continue to point toward human activity as the predominant cause of observed climate and ecosystem changes. Observed ecological effects include changes in migration patterns, the disappearance of species in particular locations, and the lengthening of growing seasons in temperate and northern regions.

This new evidence falls well within the range of earlier projections, but the nature and rate of observed changes has led some IPCC participants, including current IPCC chair, Rajendra Pachauri, to suggest that the effects of global warming on climate and ecological systems has been greater than expected and to speak forcefully in support of stronger efforts to curtail greenhouse emissions.

What do scientists project about future warming and its effects?

Projections instead of predictions

There is currently no effective way to recapture greenhouse gases on a significant scale once they are released. From a policy perspective, this calls for predicting the future with as much certainty as possible. From a scientific perspective, making predictions about a system as complex as the climate is not possible for several reasons.

Complexity

The earth's climate system is exceedingly complex. Determining global temperature and sea level is not a simple matter. Determining how one factor affects others is more difficult and subject to differing standards of evidence and interpretation. Predicting what will happen in the future is even more complex because predictable changes will have unpredictable effects. The IPCC makes its projections in numerical ranges because known uncertainties make more specific predictions unwarranted for many reasons.

One is that greenhouse gases vary greatly in the amount of time they are apt to remain in the atmosphere, from a few hours or days for ozone, to thousands of years for some synthetic chemicals. Carbon dioxide, the predominant greenhouse gas, remains in the atmosphere for 50 to 100 years, so the full effect of the carbon dioxide currently being released cannot be known until between the middle and end of the century.

Another is that the climate system is known to have self-regulating features (negative feedbacks), destabilizing features that amplify small changes (positive feedbacks), and features whose overall effects are not known or knowable (indeterminate feedbacks). Higher carbon dioxide concentrations in the atmosphere are moderated by increasing uptake by the oceans and vegetation. Less snow cover due to warmer temperatures reduces the reflection of sunlight and contributes to warming temperatures. Warmer temperatures may lead to more clouds, which both reflect light and trap heat, but it is not possible to know in advance what kinds of clouds will form, and whether the net effect will hasten or slow the warming trend.

However, the most uncertain feature of the future climate system is the nature and scale of future human activity. Will societies manage to restrain their industrial and agricultural emissions, or will the emissions continue to increase until their effects provide a negative feedback by disrupting industrial and agricultural production? As a result, climate scientists tend not to make specific predictions, but to make a number of projections based on different "scenarios" of self-regulating and amplifying interactions and future human activity. These projections are derived from exceedingly sophisticated models of the climate system that are created and "run" on super-computers. The IPCC consensus assessment incorporates the results generated by these climate models.

Projections in the 2001 Assessment

In its most recent report, the IPCC assumed that a carbon dioxide equivalent of about 550 ppm, a doubling of the pre-industrial level, will occur by 2050. This level entails about 450 ppm of carbon dioxide plus the effects of the other greenhouse gases. The IPCC concludes this would lead to a rise in global temperature of between 2.4 and 10.5 F degrees by 2100. They anticipate that land surfaces and higher latitudes will experience larger increases.

Sea level is apt to rise between 10 and 30 inches by 2100. Wetlands will be flooded. Many low-lying regions and small island states will have to be evacuated due to storm surges and saltwater intrusion. Evaporation and precipitation will increase about 1% for every 1 F degree temperature rise, and their distribution will be increasingly uneven and unpredictable. There will be more frequent and severe heat waves and droughts, and heavier storms and floods. Rapid climate change will limit the ability of many plant and animal species to adapt. Insects, rodents, disease organisms, and other species that reproduce rapidly will increase.

In its First Assessment in 1990, the IPCC estimated that to stabilize atmospheric CO2, global emissions must be reduced below 1990 levels by at least 60%. Temperature will continue to rise for many years after emissions are reduced and greenhouse gas concentrations stabilize. Sea levels will continue to rise for several centuries.

Evidence since the 2001 Assessment

Climate modeling is based on the interactions among gradual linear changes of many variables in the existing system. The modeling is not able to account for the possibility that the accumulation of particular changes would reconfigure the whole system. These have been termed "climate surprises." There are three prominent "surprise" scenarios.

One involves the underlying pattern by which water circulates through the earth's oceans. At present, cold salty water flows into the North Atlantic from the Arctic Ocean and sinks when it meets warmer, less salty water carried from the tropics by the Gulf Stream. This is the "engine" that drives the Gulf Stream and deep ocean currents that feed it. The result for Western Europe is a much warmer climate. Melting of snow and ice in the arctic region is reducing the salt content of the water in the North Atlantic. If this process continues, water entering the North Atlantic may no longer sink, and the oceans' circulatory pattern may become very different. There is evidence to suggest that this happened several times before, with a rapid change to a much colder climate.

A second potential "surprise" is the rapid release of huge quantities of methane from arctic tundra as it thaws and from frozen arctic waters. The addition of large quantities of a powerful greenhouse gas to the atmosphere would rapidly accelerate global warming and further destabilize climates. The integrity of complex ecosystems depends on climate stability. Climate instability challenges ecosystem resilience. Weather extremes - of heat, cold, drought or flooding - devastate biotic communities as they devastate human communities.

The third potential "surprise" scenario is the rapid disintegration of Antarctic and/or Greenland ice which could raise sea levels by many feet within just a few years. Many of the world's cities, industrial areas, agricultural lands, and wetlands habitat would be inundated.

Several years ago, these "surprises" were viewed as possibilities in several centuries. Evidence of rapid warming in the arctic regions, and evidence that rapid change has occurred in the past has led them to appear more conceivable, though not probable, before the end of the century.

The other issue that has raised by recent evidence of climate and ecosystem disturbance is how much global temperature can rise before the capacity of large scale ecosystems to survive is exceeded. Some analysts have suggested that a 2 C degree rise ( 3.6 F degree) above the 1990 average may be as much as many ecosystems can withstand. To prevent greater increases, they say it may be necessary to hold or return carbon dioxide concentrations to 400 ppm, rather than 450 ppm that was the IPCC's target in the 2001 Assessment.

Why has there been controversy about what is known and projected?

Corporate interests

In 1990, a number of large corporations formed the Global Climate Coalition to oppose the conclusions of the IPCC. The Coalition funded and publicized the work of a few scientists who challenge its findings, and hired public relations firms to spread doubt about the IPCC's credibility. As a result of these efforts, news reports have tended to present "both sides," and make it seem as though there is much more disagreement among climate scientists than really exists.

In response to the IPCC's 2001 Assessment, many of the original members of the Global Climate Coalition have disassociated themselves from those efforts, and the Coalition has disbanded. However, Exxon-Mobil Corporation, Western Fuels Association, representing coal interests, and other wealthy parties continue to fund public relations efforts to dispute the IPCC findings. Those who represent the views of the Global Climate Coalition now control the US Presidency and are a powerful influence in the US Congress.

Soon after the IPCC's 2001 Assessment was released, it was reviewed by a panel of the National Academy of Sciences at the request of President Bush. Although the National Academy's review supported the scientific foundation of the IPCC report, and concluded that "global warming is undoubtedly real," the Bush administration and some members of Congress continue to be critical of the IPCC's findings. One, Senator James Inhofe of Oklahoma, refers to global warming as a massive hoax.

Discontinuities in realities and expectations

Ecological economist Herman Daly refers to philosopher Alfred North Whitehead's identification of one's pre-analytic vision in shaping one's interpretation of evidence. With regard to climate change, opinions seem to be heavily influenced by distinctive pre-analytic visions of the human-earth relationship as it is and as it should be.

There are of course many pre-analytic visions, some of which are highly nuanced. One common vision views the earth as the environment in which human ingenuity and progress can flourish. Environmental limitations are challenges to be met and overcome. This view focuses on faith in the ability of technology to solve whatever problems arise as a result of human progress.

A contrasting vision views industrial societies as the adolescents of their biotic communities who want to flee the constraints of the nest, but have no place to go. This view focuses on the earth's bio-physical limitations, and the need for all human societies to adapt to them.

The burden of proof

Opinions are shaped by assumptions that are rarely articulated about who must prove what. In a criminal court, the burden of proof lies with the prosecution, and the protection of a reasonable doubt favors the accused. In a civil court, decisions are based on the balance of evidence.

With regard to greenhouse gas emissions and their effects, who is the prosecution? and who stands accused and receives the protection of a reasonable doubt? There would appear to be three parties: those whose job it is to provide a profitable return to investors, those whose job it is to provide for the general welfare of the electorate, and those who are of the view that the well-being of the earth's biotic community is essential to human well-being, that the long-term well-being of the earth's biotic community is of a higher priority than the short-term well-being of industrial society.

At present, the protection provided by a reasonable doubt lies with those whose job it is to provide investors with a profitable return. The burden of proof lies with those who advocate for the general welfare of the electorate. The balance of evidence seems unpersuasive to the political process as a whole. Those who place a priority on the long-term well-being of the living earth, the "integrity of creation," are for the most part in the audience. Perhaps this is not as it should be.

Why should Friends be concerned?

What greater sacrilege could there be than to knowingly and wantonly participate in unraveling the fabric of life on Earth as God creates it?

What can Friends do?

Philadelphia Yearly Meeting recently held a Called Session on Climate Change, which united in a minute, incorporated in an Epistle, that includes "holding Friends lovingly accountable" which means we must discern what this means. Most us are already "doing something" and know of many more things we could do.

Let us ask ourselves how, as a faith community, we can come under the weight of the disfunctional human-earth relationship in which we are enmeshed, of which climate change is but one of the most pressing manifestations. How can we support one another in our monthly meetings, churches, and worship groups, in taking more of the steps already known to us? How can we, together, seek ways as yet unknown to capture the attention of the larger society about the promise of redemption if we are willing to change?