What this Blog is About

WHY READ THIS BLOG?

I’m worried about the world we live in. It’s a world in which science and technology play a major role, and individual, public and political decisions are going to determine our future safety and health. In order to make decisions, the deciders (whether voters or members of Congress) need facts. Where these facts come from is the source of the problem I want to blog about. 

How do people come by their facts? Is there a difference between fact and belief? I could spend a lot of time on the philosophy surrounding this question, but I don’t want to. I want to deal with important current issues where belief and reason are at odds.

In the posts that follow, I will write about 

    Climate Change (specifically, Global Warming), and the conflict between science and politics
    The move to teach Creationism in the public schools as an alternative to Darwin's Theory of Evolution, and the conflict between science and religion
    The allegations that the measles vaccine can cause autism in children, and the conflict between science and the media. 

In the first posts that follow I'll begin with Global Warming.

GLOBAL WARMING

Science vs Politics: Climate Change

I am just a poor boy.
Though my story's seldom told,

I have squandered my resistance

For a pocketful of mumbles,

Such are promises

All lies and jest

Still, a man hears what he wants to hear

And disregards the rest.

                                                                      The Boxer, Paul Simon

 

I have to admit that I bring to this particular topic a sense of futility and anger with the people to whom we've given the power to control our future. An example of this is James Inhofe, an elected member of the United States Senate, expected to take over the Senate Environment and Public Works Committee. He’s a Republican from Oklahoma, who has been calling global warming a “hoax” for years—that’s nothing new. He claims that the idea that man-made pollution could affect the climate is “arrogance,” because, as he believes we all know, only God can affect the climate.

As he puts it in his own words:

Well actually the Genesis 8:22 that I use in [my argument] is that “as long as the earth remains there will be springtime and harvest, cold and heat, winter and summer, day and night.” My point is, God’s still up there. The arrogance of people to think that we, human beings, would be able to change what He is doing in the climate is to me outrageous.

That’s scary.  I’m not against the democratic process. But our elected officials don’t always come up to the demands of the position.

Pete Seeger wrote a song about this. You can listen to it at this link  but here are the relevant words:

What did you learn in school today,


Dear little boy of mine?


I learned our government must be strong.


It's always right and never wrong. 


Our leaders are the finest men.


And we elect them again and again...

OK. I got that off my liberal chest! Let’s move on.

Climate Change is occurring.

There is a lot of denial of this fact. Some of this denial is out of ignorance, and some is deliberate. I want to provide the reader an opportunity to examine the facts and how they were obtained. I want to examine false and misleading beliefs, and how to make a judgment between fact and belief.

The question of whether the Earth is warming on a global scale has become quite heated, and serves as an avenue for discussing the conflicts between belief and fact, and specifically in this case the interactions of politics and science. In several posts that follow I want to outline the science relevant to long-term changes in climate, discuss the evidence that global warming is occurring and that human-controlled factors play a major role, and consider the attacks mounted by those who believe that global warming is a scheme of the “radical environmental movement” (quoting Sarah Palin) as revealed by the “climate e-mail scandal” (Palin again) which exposes “fraudulent scientific practices” (more Palin).

Let’s not deal with revelation at this stage. Let’s look at some everyday facts. The temperature of the Earth’s surface varies dramatically from one locale to another, and often from day to day in any one place. In San Diego, California, the seasonal extremes of daily temperature are roughly from 40°F to 100°F. In my previous home in Amherst Massachusetts the range is greater, perhaps from -10°F to 95°F. Scientists investigating Global Warming are concerned about possible temperature rises of just 2 to 4°F. What’s the big deal?

First, we have to differentiate between “weather” and “climate.” Weather deals with the instantaneous state of the atmosphere at some specific place on the earth. If I say there was, or will be a thunderstorm in London on Thursday afternoon, that's a statement about the weather, either observed or predicted. But climate deals with longer time scales and with average temperatures and other statistics over both space and time. If I say London next summer will be drier and warmer than usual, that's a statement (in this case, a prediction) about climate.

A key concept here is that climate deals with long time scales. Weather is a short-time-scale event. The significance of this difference is that life in a particular place can deal with short-time-scale variations. If the temperature rises or falls 20°F during a day, humans can seek shelter, put on more appropriate clothing, or even suffer through the heat or cold for a few hours. And while a sudden overnight frost could damage a farmer’s fruit crop and lead to significant financial effects, more generally the flora on earth survive unexpected changes in weather. And because weather changes occur over short time scales, people can moderate the effects of sudden changes in weather, with shelter and appropriate clothing. Animals and plants have developed natural means of protecting themselves from sudden temperature changes, such as a thick layer of fat or the bark of a tree.

On seasonal time scales, many animals respond to the onset of winter by hibernating or migrating. Annual plants may die off from the onset of a prolonged cold period, but they may produce seeds that are protected against the cold and that yield the next generation of the species when the “growing season” arrives. Trees survive harsh winters to leaf out again in the spring. Through millennia of evolutionary adjustments, “nature” has developed mechanisms to insure survival against short-term (seasonal) variations in weather.

The concern is not with the weather. The concern is with the longer-term changes in the climate of the earth. We begin with a few basic questions.

1: Is the earth’s climate changing?

2: If so, is that due to human actions?

3: What is the scientific consensus on climate change?

An analysis of the abstracts (short summaries) of nearly a thousand scientific publications in the peer-reviewed literature (over the ten-year period 1993 to 2003) shows that the vast majority of scientists agree with the IPCC (Intergovernmental Panel on Climate Change), the National Academy of Sciences, and the public statements of their own professional societies: global warming is happening, and humans are contributing to it. Politicians, economists, journalists, and others may have the impression of confusion, disagreement, or discord among climate scientists, but that impression is incorrect. 

This acceptance of scientific evidence, (we will need to define “scientific evidence,” and examine evidence later) widely held within the science community, continues to the present. On October 21, 2009 a letter to members of the U.S. Senate was sent by the American Association for the Advancement of Science. 

The American Association for the Advancement of Science (or AAAS) is an international non-profit organization with the stated goals of promoting cooperation between scientists, defending scientific freedom, encouraging scientific responsibility, and supporting scientific education and science outreach for the betterment of all humanity. The AAAS is the world's largest general scientific society, with over 100,000 individual and institutional members, and it is the publisher of the well-known scientific journal Science. 

The letter, endorsed by the leaders of 18 scientific associations, follows.

Dear Senator:

As you consider climate change legislation, we, as leaders of scientific organizations, write to state the consensus scientific view. Observations throughout the world make it clear that climate change is occurring, and rigorous scientific research demonstrates that the greenhouse gases emitted by human activities are the primary driver. These conclusions are based on multiple independent lines of evidence, and contrary assertions are inconsistent with an objective assessment of the vast body of peer-reviewed science. Moreover, there is strong evidence that ongoing climate change will have broad impacts on society, including the global economy and on the environment. For the United States, climate change impacts include sea level rise for coastal states, greater threats of extreme weather events, and increased risk of regional water scarcity, urban heat waves, western wildfires, and the disturbance of biological systems throughout the country. The severity of climate change impacts is expected to increase substantially in the coming decades. If we are to avoid the most severe impacts of climate change, emissions of greenhouse gases must be dramatically reduced. In addition, adaptation will be necessary to address those impacts that are already unavoidable. Adaptation efforts include improved infrastructure design, more sustainable management of water and other natural resources, modified agricultural practices, and improved emergency responses to storms, floods, fires and heat waves.

We in the scientific community offer our assistance to inform your deliberations as you seek to address the impacts of climate change.

While there is room for continued debate on the details, it is fair to state that the vast majority of scientists trained in the research methodologies of geophysics, climatology, meteorology, statistical analysis, etc., now believe, on the basis of measurable scientific evidence, that global warming is occurring and that it is largely anthropogenic [man-made]. Unfortunately, the Senate of the United States does not accept this science-based and hugely documented opinion. Actually, nearly all Democrats believe this, and nearly all Republicans either deny the facts, or are unwilling to go on record against their party's stand. Climate Change is not a political, ideological issue. See the following report of this recent (January 2015) Senate vote .

We should turn then to the next questions:

What is the evidence that warming has already occurred? What is the extent of anticipated (predicted for the future) changes? What is it that gets “warm,” and by how much? How soon?

Before going there however, let’s look at the physics of climate change, and in particular the chemical and physical factors that control the temperature of the earth. We begin with the Greenhouse Effect.

Factors that Effect the Earth's Temperature

The Greenhouse Effect

To understand global warming we have to begin with a few ideas about radiation. The word "radiation" is loaded with negative connotations: we have to be careful about getting too many X-rays from medical examinations. Too much sun exposure (solar radiation)  can damage the skin and cause cancer. 

But any object emits some kind of radiation to a degree that depends in part on how hot it is. What we see when we observe an object is the light emitted (radiated) from the object that the retinas of our eyes process into an image (a picture) of the object. What we see, and what we call “light,” is called electromagnetic radiation. 

Different colors correspond to different wavelengths of electromagnetic radiation, just as different keys on a piano produce sounds of different wavelengths. 

What we feel as heat from the Sun is actually solar radiation. Some is visible, but some is in the infrared or ultraviolet range of wavelengths, which cannot be detected by the human eye. 

When solar radiation hits the outer atmosphere of the earth, some portion of this energy is reflected back into space by the earth's atmosphere. Another portion is dispersed and scattered by the molecules in the atmosphere and this reduces how much gets through to the surface.  

But a large portion of solar radiation passes through the earth's atmosphere to reach the earth's surface. The radiation reaching the earth's surface is largely absorbed resulting in surface warming. 

The roof of your car absorbs solar energy and gets hot to a degree that depends on the material it is made of, and upon its color. Since it is hot, it radiates energy. 

This re-radiated solar energy is now in longer (infrared) wavelengths because as hot as the roof might be, it is a  lot cooler than the sun!  

As this radiation leaves the surfaces of the earth (whether the roof of your car or the vast surface of the oceans), it once again interacts with the atmosphere. 

Some of this re-radiated energy escapes to space, but much of this re-radiated energy is absorbed by molecules in the earth's atmosphere and re-radiated back to the earth's surface. 

On a smaller scale, this is similar to the warming that occurs inside your car parked in the sun. In the case of the car, the window glass passes solar radiation into the car easily (because glass is very transparent to sunlight), but the re-radiated energy does not pass out easily through the glass and so is “trapped” (absorbed) in the car. 

The glass windows behave toward the car (in controlling how much the interior of the car heats up) in the same way that the  atmosphere behaves toward the earth, controlling how much the earth heats up. 

In the atmosphere, the molecules responsible for retarding the escape of the re-radiated energy (which is called “radiation trapping”) are called greenhouse gases, and the major ones are water (H₂O), nitrous oxide (N₂O), methane (CH₄), and carbon dioxide (CO₂). 

These greenhouse gases act like the glass in a greenhouse, letting sunlight in but trapping re-radiated energy inside. 

Without these gases most life on earth would not be possible, because the surface temperature of the earth would likely be about 60°F colder. 

So the greenhouse gases actually make the Earth hospitable to life. 

But too much greenhouse gas will cause the Earth's temperature to rise to a degree that has harmful consequences. We have no problem living in places where the weather changes by 60°F from one season to another. Why would life be impossible if the earth’s surface were 60°F colder? 

Suppose the earth’s surface were only 20°F colder, or 20°F warmer; would life be possible? Scientific evidence leads to predictions that if the earth’s surface temperature were to rise globally by only a few degrees, over a sustained period of time, the impact on life would be immense and in some places catastrophic!

In essence, greenhouse gases act like an insulator or blanket above the earth, keeping the heat in. 

Increasing the concentration of these gases in the atmosphere increases the degree to which the atmosphere blocks the escape of infrared radiation. 

Over several hundred thousand years, up to the present time, the level of greenhouse gases in the atmosphere has made life on earth sustainable. 

But too great a concentration of any of the greenhouse gases can have dramatic effects on climate and significant repercussions upon the world around us. 

The Energy Budget

Put a pot of water on the stovetop and turn on the heat. The water gets hot, of course, because of the heat input through the bottom of the pot. 

But there are heat outputs (losses) from the pot that retard the rate at which the water heats up. For example there is radiation of heat away from the hot sides of the pot. 

After a while, steam begins to rise from the surface of the water, and the escape of the steam also carries heat away. Put a lid on the pot and retard the heat loss due to steaming. 

The rate of warming of the water in the pot is a consequence of the “heat budget” for the process—the imbalance between heat input and output. 

The earth also has a heat budget.

Solar radiation is the external source of the earth’s heat. Some of that input is reflected by clouds, some is absorbed by gases in the atmosphere, some is absorbed by the earth’s surface and some is reflected back to the atmosphere by the surface. 

Different regions of the earth, and day-to-day weather variations have a strong effect on these absorptions and reflections. Ocean, sand, snow, clouds, all contribute in different ways to the earth’s energy budget.

In order to study climate change it is necessary to make measurements that “average out” regional and seasonal changes. 

Although the statistical procedures used to create these averages leave room for critique of the statistical methodologies, as well as of the methods of measuring temperatures of the land and the sea, the worldwide science community has produced widely accepted methods of making these measurements. 

This is the basis for exploring the question of whether the earth’s temperature is changing in a global sense, or in a particular region, and whether this is due to man-made changes in the environment that must be reversed.

The Evidence of Global Warming

Scientific Evidence

Increasing Temperatures & Greenhouse Gases

Through the study of ancient ice cores from Antarctica it is possible to compare atmospheric concentrations of one of the key greenhouse gases, carbon dioxide (CO₂), with temperature variations over the past 400 thousand years of the earth's history (figure below).

The two trends are clearly related to each other, with fluctuations in one plot almost exactly mirrored in the other for more than 400,000 years. 

But suddenly in the 1800s, as the Industrial Revolution takes off, atmospheric CO₂ concentrations begin an unprecedented upward climb, rising rapidly from 280 ppmv (parts per million by volume) in the early 1800s to a current level of about 400 ppmv, well above the highest concentrations previously attained in the course of the preceding 400,000 years. 

Notice how CO₂ concentration (the upper line) seems to rise vertically at the end of the time series, as "now," the present time, is approached.  The increase appears vertical because of the large time scale, but it actually occurs over the past 150 years, which corresponds to the age of fossil fuels (the modern industrial age). This is the primary evidence of the long-term relationship between CO₂ concentration in the atmosphere, and the earth’s temperature.

On a shorter and recent time scale, direct measurements of CO₂ concentrations in the atmosphere show the sharp upward rise of the past decades. This is shown in the figure below. (The red squiggles reflect the day to day variations, but month by month the average value of CO₂ concentration increases, and the year by year trend is clear.)

The main point of contention regarding the reality of Global Climate Change and the claim that it is a consequence of increased man-made emissions of greenhouse gases—primarily CO₂—lies in the scientific evidence (examples of which are presented above) that the earth is warming, and the conclusions reached by several independent groups of scientists that there is a cause and effect connection between observed temperature changes and CO₂ concentrations measured over an extended period of time.

We turn now to the next issue: The gathering of data on global warming, from land and sea and polar ice. The analysis of the data is an enormous task involving a large number of scientific establishments. How is this task coordinated, monitored, and evaluated?

The Intergovernmental Panel on Climate Change (IPCC)

The data presented above, clearly showing a relationship between CO₂ and the earth’s temperature, does not of itself prove a causal relationship. 

Upon noting these indications of global warming, and recognizing the potential for dramatic changes in the climate due to continued unchecked accumulation of greenhouse gases in the atmosphere, the World Meteorological Organization (WMO) and the United Nations Environment Program (UNEP) established the Intergovernmental Panel on Climate Change (IPCC) in 1988. 

The purpose of the IPCC is to objectively review existing and developing peer-reviewed scientific literature to form an objective evaluation about the risk of human-induced climate change. 

There are two key points here. The data and analyses considered must have appeared in peer reviewed scientific journals, and hence have already been subjected to the criticism of knowledgeable scientists. And the reviewers must be objective, free of commercial and political bias. Objectivity is not always easy to evaluate and ensure. 

Subjecting a proposed scientific paper to multiple reviewers makes it easier to eliminate bias from the peer review process.

What is the Peer Review Process?

The peer review process varies from one scientific publication to another, but in general it goes like this. A manuscript is submitted to a journal for publication. The editor of the journal selects several (typically three or four) individuals who are acknowledged experts in the field of study. 

The reviewers might include, depending on the topic of the manuscript, chemists, climatologists, statisticians, and/or others whose expertise is essential to evaluating the reliability of the scientific study and its conclusions. 

The reviewers respond to the editor, point out any errors or weaknesses in the work, and recommend publication if the noted errors/deficiencies are corrected. A reviewer may recommend outright rejection of the manuscript as unsuitable for publication. 

The set of reviews is transmitted by the editor to the author(s) of the manuscript, and they may make recommended changes, or they may argue that the reviews include unfair or incorrect criticism. 

The editor makes a judgment as to whether the revised manuscript (or the author’s rebuttals) has dealt with the reviewers’ comments. (Journal editors are usually highly regarded scientists in the fields covered by the journal. 

Most journals have a panel of editors with expertise in various aspects of the particular field(s) covered by the journal.) The editor may send the revised manuscript back to the reviewers for another assessment. 

In some cases, the editor may ask an additional reviewer to give an opinion on the author’s rebuttal of a particular point in the reviews.

After years of investigation and in consultation with thousands of scientists, the IPCC was able to write, in its Second Assessment Report in 1995, that climate has changed over the past century and that the twentieth century had a mean temperature “at least as warm as any other century since 1400 A.D.” 

Their report concluded that the dramatic increase in carbon dioxide concentration in the atmosphere over the past 150 years (noted above) is largely due to anthropogenic (human-caused) effects and further concluded that “the balance of evidence suggests a discernible human influence on global climate.” 

The predictions of mathematical models presented in the report indicated future temperature rises in the range of 1.8 to 6.3 degrees Fahrenheit in the global mean surface temperature during the next century, with sea-level rises predicted to be in the range of 6 inches to 3 feet by 2100.

You can see that these predictions vary widely. In part, this is due to varying assumptions made about what corrective steps might be taken by various governments in the future. 

The variations also reflect the real uncertainties in our current understanding of the physics of climate change. Detractors of the global warming scenario use this as an argument to disregard the results of warming models. They fail to note that even the low end of predicted changes is of significance, and warrants action. 

Disagreement in the science community about how much warming may occur in the future does not imply that significant warming will not occur.

The conclusions of the IPCC gained broad support in the world scientific community and, in the summer of 1997, a letter signed by 2,600 scientists called for the United States to take a leadership role in reducing greenhouse gas emissions to diminish the likelihood of intense, continuous global warming. 

Improved Models, Growing Confidence

The Third Assessment Report of the IPCC was released in 2001, incorporating new research undertaken in the five years since the Second Assessment Report. Increased confidence in evolving modeling techniques lent added weight to the linkage between rising temperatures and continued greenhouse gas accumulations.

Based on the large amount of evidence reviewed by scientific experts on the Panel, the IPCC's 2001 report stated emphatically that "concentrations of atmospheric greenhouse gases has continued to increase as a result of human activities." 

More recent revised models of the future predict by 2100 even higher anticipated temperature increases than did the First Assessment Report (under different likely scenarios), while estimates for sea-level rise, though still significant, decreased slightly with refinements to the models used.

The most recent report of the IPPC (2014) can be found on the following website: http://ipcc.ch/   where you can examine various details of the report.

To summarize to this point, it is apparent that the vast majority of members of the scientific community, specifically those people trained and experienced at obtaining and analyzing experimental observations relevant to climate and its impact, agree that global warming is occurring, and it is caused by worldwide man-made releases of greenhouse gases into the atmosphere. 

Let’s turn then to the next topic: the impact of Global Warming.

The Impact of Global Warming

What is the impact of these changes in global temperature?

Twenty years ago the scientific community provided evidence and warnings that a global climate crisis was impending, that it was largely man-made, and there were means to slow or reverse the expected consequences. 

In those twenty years, very little action has been taken to significantly reduce the magnitude of the global crisis that we face!

The crisis I'm referring to is the steady rise in the temperature of the earth on a global scale. The observed rise is only a few degrees Fahrenheit, and the predicted future rise is similar: a few degrees. 

This is what we refer to when we talk about Global Warming.

One of the obvious questions to begin with is this: why is there any concern about a rise in temperature of a few degrees? We live through weather changes of tens of degrees every day and every week. How can such a small temperature change be harmful? 

In this post I want to summarize the analyses of thousands of scientists on the impacts of such a small global temperature rise.

Let's begin with a very simple example of these analyses and conclusions.

Increasing global temperatures are harmful because they cause an increase in the volume of the seas. They also cause the icecaps to melt, and both of these conditions will cause a rise in sea levels. 

Why is a rise in sea levels a problem?

Sea level rise increases the vulnerability of coastal populations to flooding and causes land to be lost to erosion. Sea levels have risen 4 to 10 inches this century and are predicted to rise another 6 to 37 inches in the next century. 

Hundreds of thousands (and possibly millions) of people will have to relocate and be accommodated by other countries, with consequent political, economic and social impacts on those countries.

Where do these numbers, and predicted consequences come from?

In response to the accumulated evidence being produced by highly respected and qualified scientists around the world, an Intergovernmental Panel on Climate Change (IPCC) was created, which is made up of thousands of climate scientists from around the world. (Go to this link if you want to get an idea of the range of topics studied in relation to climate change.) 

These scientists have been making measurements of changes in the temperature and chemical composition of the earth's oceans and atmosphere. 

Mathematical models have been developed that lead to predictions of the future chemical and physical state of the atmosphere and oceans, and the subsequent effects on the earth's climate. Their methods have been subjected to continual analysis and improvement in order to produce the best possible predictions of climate change, and the consequences of climate change. (Later in this post I will provide some links to reports issued by the IPPC.)

In addition to sea level rise, another consequence predicted by these scientists, one  that will follow the rise of the temperature of the earth's oceans, is an increase in the frequency and intensity of storms such as monsoons and hurricanes.

Think about Katrina. Katrina was not a Global Warming event. However, strong storms in coastal areas can be devastating. 

There are currently 46 million people around the world who are at risk due to flooding just from the storm surges that follow intense weather events.

Yet another consequence of Global Warming will likely result in an increase in the amount of water exchanged among the oceans, atmosphere, and land. 

Increasing rates of evaporation will likely result in drier soils in some regions, (such as the American Southwest) and larger amounts of precipitation and more frequent and severe droughts and floods in other areas. 

This prediction has rung true already. In the early '90's, two "100-year floods" (this means floods that are only expected to occur once every one hundred years) occurred in less than 5 years in the Midwestern United States. 


Regional water resources will likely be dramatically impacted by changes in availability, distribution, and supply.

A warming earth will most likely have a range of largely negative impacts on human health. This will  be caused in part by more frequent extremes in temperature.

An increase in mortality from heat stress is likely (e.g. 465 deaths in Chicago during the hot summer of 1995). 

Again, there is no claim here that this particular event was caused by Global Warming. The point is that more frequent thermal extremes predicted in the IPCC reports can have tragic consequences, of which the Chicago mortality is just an example.

As a result of warming on a global scale, there will likely be an increase in the geographical range of insect transmitted diseases such as malaria, dengue, yellow fever, and encephalitis. 

Currently, 45% of the world's population is within the zone of potential malaria transmission. With predicted temperature increases, there will likely be an additional 50 to 80 million cases of malaria worldwide, bringing the percentage of the world's people living within the susceptible zone from 45 to 60%.

It is also likely that increasing temperatures will result in increases in the abundance of air pollutants, such as pollen, and mold spores, with a resulting decline in air quality. (Molds grow best in warm damp and humid conditions, and spread and reproduce by making spores.) 

An increase in the number of cases of respiratory disease, asthma, and allergies is likely to follow. 

The change in the frequency and intensity of extreme weather events will cause floods which contaminate water supplies. Combined with warmer atmospheric temperatures this will lead to the growth of bacteria and the subsequent spread of disease.  

In the next 100 years between one third and one half of the world's mountain glaciers could disappear. This would greatly reduce the water supply to rivers and thus hydroelectric dams (electric power generation) and agriculture. 

Paleoclimate (past climate) data and models show that changing atmospheric temperatures also cause major changes in ocean circulation. Such changes in ocean circulation can result in rapid and dramatic changes in climate.   

Total global food production is not expected to change substantially as a result of climate change, but production will probably change dramatically regionally. Some areas will have increasing crop yields. Others will decline, especially in tropical and subtropical regions. 

The variety of crops that can be grown in a region is predicted to decline.  Developing countries that currently struggle with these issues will suffer even more.

These summaries of just a few of the projected effects of Global Warming, as presented above, are based on IPCC Technical Assessment Reports (TAR) issued periodically. 

These reports are intended to assess scientific, technical and socio-economic information concerning climate change, its potential effects, and options for adaptation to and reduction of the effects. 

Here is a link to the most recent report (the largest and most detailed summary of the climate change situation ever undertaken), involving thousands of authors from dozens of countries, and the report states in its summary,

Warming of the climate system is unequivocal.

Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic (man-made) greenhouse gas concentrations. In the public arena the focus has primarily been on carbon dioxide, largely because CO₂ is the product of our energy and transportation technologies, and as such is potentially controllable through new technologies that emit less or no CO₂ .

Additional recent reports (See the EPA report on the effects of global warming on health:  http://www.epa.gov/climatechange/effects/health.html ) provide updated projections based on improved climate models, but the lesson is unchanged. 

Global warming is real, it is caused by man, and its consequences, if not reversed, have the potential to be serious, and in some cases disastrous. 

It is possible for governments to take steps to mitigate the impacts of some of these threats.