Global warming. The term has become a part of our everyday vocabulary over the past few decades. In June 1988, NASA climate modeler Dr. James Hansen testified before the U.S. Senate that he was "99% certain" that global warming was taking place. His testimony touched off a lot of media attention and caused the "man on the street" to consider what since then has become a complicated and even emotional environmental issue. The public has been swamped by media reports covering a number of other reportedly global warming-related (in a fuzzy sort of way) phenomena: the greenhouse effect, increases in greenhouse gases, the ozone hole, major El Niño events, sea-level rise, melting glaciers, intense hurricanes, floods, droughts, summer heat waves, and on and on. The five warmest years in the modern global mean temperature record have all occurred in the 1990s; 1997 was the warmest year to date, and after its first 10 months, 1998 was poised to shatter 1997's record. Are humans causing global warming and in effect experimenting with the global climate system? As CDIAC's resident climatologist, I'm regularly asked this question by our users who don't happen to be scientists. While there is well-documented evidence of anthropogenic effects, such as the buildup of atmospheric CO2 and decreasing stratospheric ozone levels, there is far from universal agreement on what role we may be playing in observed climate variation. It's important to realize that the greenhouse effect is a naturally occurring phenomenon; atmospheric water vapor, clouds, and other trace gases trap heat near the surface and keep the planet much warmer than it would otherwise be without an atmosphere. The multibillion dollar question is: Are rising greenhouse gas concentrations strengthening this effect enough to artificially warm the planet?

Since 1988, climate scientists from around the world have worked together under the auspices of the Intergovernmental Panel on Climate Change (IPCC) to try to answer this question. One conclusion is that global mean surface temperature has risen roughly 0.5°C (~1°F) over the past century. A recent IPCC report, Climate Change 1995: The Science of Climate Change, stated, "The balance of evidence suggests a discernible human influence on global climate." This caused quite a stir, for not all in the scientific community agree that the evidence supports this statement; some feel we are mainly witnessing natural climate variability. There are even those scientists who feel increasing atmospheric CO2 and any resultant warming may not be a bad thing, because of experimentally demonstrated benefits for plant growth and likely increases in growing season length. The next IPCC report is due out in 2001. Stay tuned.

So, are we getting any closer to being able to say with absolute certainty that we are altering earth's climate (i.e., causing global warming)? I think most would agree that a considerable body of evidence is mounting, but there is still much to be done in observing, analyzing, and modeling the climate system before the debate will be laid to rest. In the meantime, we at CDIAC will continue to do our best to ensure that critical, quality-assured, global change databases are made available to researchers, policymakers, educators, students, and the interested lay public. Keep a special eye out for ever-expanding holdings in our online TRENDS publication (

We at CDIAC often use the Internet just as you do (i.e., to seek out information of interest to us in our work). A Web search on "global warming" or "climate change" will generate tens of thousands of hits. We've recently compiled a list of outstanding global climate change links that we hope you will find informative in your study of this issue ( We'd be glad to hear from you if you know of any high-quality links we've left off the list. Thanks.

Dale Kaiser
CDIAC Deputy Director and Task Leader for Global Change Data

CDIAC Communications | Reference Materials for Oceanic Carbon Dioxide Measurements | CDIAC's Corner | Trends Online | The International Year of the Ocean | New NDPs | Awards | Popular Updates | Selected Translated Abstracts of Russian-Language Climate-Change Publications | New Databases | Databases Currently Available | Recent and Relevant | CDIAC's Bookshelf | Global Change Education Program | Related DOE Programs |

kng 01/99