Humans do cause climate change

I noticed several inaccuracies in the letter sent by Dr. Thomas P. Sheahen titled: “Scientists divided on issue of global warming” (CR, April 26). In this response I will address Dr. Sheahen’s comments on the consensus of scientist’s concerning human-induced climate change and his comments on recent global temperatures as compared to those of the last millennium. I feel that responding to this letter is important since there may be readers of The Catholic Review not familiar with the technical literature in this subject area.

An essay titled “The scientific consensus on climate change” was published in the Dec. 3, 2004, issue of the journal Science, which addressed the issue of human-induced global climate change. As discussed in that essay, of the 928 articles published in refereed scientific journals between 1993 and 2003, 75 percent of the papers explicitly endorsed the position of human-induced global climate change or took it for granted in evaluating impacts or proposing mitigation approaches. Of the 928 papers, 25 percent dealt with research methodology or climate change prior to human activity, thus not taking a position on current human-induced global climate change. Remarkably, none of the 928 papers disagreed with the position of human-induced global climate change. The conclusion drawn was that “despite claims sometimes made … that there is not good evidence that Earth’s climate is being affected by human activities, the scientific community is in overwhelming agreement that such evidence is clear and persuasive.”

Three significant professional societies associated with climate and environmental change research, each composed of tens of thousands of members, are the American Meteorological Society, the American Geophysical Union and the American Academy for the Advancement of Science (AAAS). In the last couple of years each of these societies has issued society level statements concluding that the evidence for human modification of climate is compelling. For example, the AAAS, the world’s largest general scientific society, released the following statement this past February: “The scientific evidence is clear: Global climate change caused by human activities is occurring now, and it is a growing threat to society.”

The international scientific community recently updated its authoritative technical compendium on climate change through the Intergovernmental Panel on Climate Change (IPCC). This panel was established by two organizations of the United Nations about 20 years ago to assess scientific, technical and socio-economic information relevant to improved understanding of climate change, its potential impacts and options for adaptation and mitigation. Hundreds of experts from all over the world have contributed to the preparation of a series of assessment reports produced by the IPCC. The Fourth Assessment Report is currently being produced and summaries of two of the three working groups are available (see In the stark language of the first working group, “it is very likely that (human-induced) greenhouse gas increases caused most of the globally average temperature increases since the mid-20th century.”
As you can see from these and many other sources there is widespread agreement by those closest to the research that human activity is causing global climate change.
Addressing Dr. Sheahen’s comment on historical temperatures, the National Research Council (NRC) was asked by the U.S. Congress in 2005 to answer the question: “How has temperature varied over the last 2,000 years?” A report titled “Surface Temperature Reconstructions for the Last 2,000 Years” was recently published by the NRC and is available to those who are interested. This report addresses the record, interpretation and accuracy of the Earth’s surface temperature for the last two millennia. Two of the conclusions of relevance here are as follows:

“It can be said with a high level of confidence that global mean surface temperature was higher during the last few decades of the 20th century than during any comparable period during the preceding four centuries.”

And “Presently available proxy evidence indicates that temperatures at many, but not all, individual locations were higher during the past 25 years than during any period of comparable length since A. D. 900.”

Out of love and concern for those who are affected by the increased severity of droughts, storms and without the resources to cope with these changes, and for those generations to follow who will inevitably be affected by the changing environment, we must learn about and act on the information gained through climate change science research.

Catholic Review

Catholic Review

The Catholic Review is the official publication of the Archdiocese of Baltimore.