lightblueline

Urgency

The last two years have seen a remarkable turnaround in public perceptions of climate change, especially in the United States. Some critical threshhold seems to finally have been breached, and we see now that both the House of Representatives and Senate are at last considering meaningful legislative proposals to deal with the anthropogenic carbon dioxide emissions that are a major cause of warming. Al Gore’s movie, An Inconvenient Truth, was clearly an important catalyst for change. Another catalyst has been the release this year of the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC: see www.ipcc.ch.) The IPCC was established in 1988 by the World Meteorological Association and United Nations Environment Programme, with a mission to assess the scientific basis for human-induced climate change, and to recommend policy options for what to do about the problem. The IPCC has released four comprehensive reports in its 19 year history, each sounding a successively more urgent warning about the impacts of fossil fuel burning on climate. Now, in its latest report, the IPCC states that most of the increase in temperature (about 0.7 °C or 1.3 °F since the start of the industrial revolution, with most of that increase in the last 40 years) is “very likely due to the observed increase in anthropogenic greenhouse gas concentrations.” In IPCC terminology, very likely means with greater than 90% probability. In 2001, the Third IPCC report had put the probability of human influence on climate at 67%. The new assessment, based on decades of intensive and increasingly sophisticated experimental observations and computer modeling, is the most authoritative statement yet, and has been a clear driver for the recent legislative initiatives. This is the good news.

The not-so-good news is that the IPCC report, while clearly necessary, is an intensely political document. The final language in the report reflects a balance of interests of the many parties involved. So this is not the consensus view of the scientific community on climate change, but rather the output of a task force given its mission by international governmental bodies, and staffed by scientists, policymakers, and bureaucrats from a broad range of developed and developing nations. For example, a key omission in the report, noted by many leading climate change scientists, is the absence of any mention of the possibility that global warming may cause catastrophic sea level rise. This has been the subject of many reports published in the leading scientific journals, which show accelerated melting from glaciers located on land. Full melting of either the Greenland ice cap, or the West Antarctic ice sheet, is projected to raise world ocean levels by about 20 feet. If this occurs, it will submerge a good chunk of the Eastern seaboard, most of south Florida and the Gulf Coast, and Santa Barbara to the limit of the Light Blue Line. And that’s not to mention the much worse consequences, in terms of the sheer displacement of humanity, that would occur in the low-lying regions of South Asia.

The IPCC report instead projects only very modest sea level rises of inches to a few feet over the next century. One can understand this based on a linear extrapolation from the increases that have been recorded so far: in the period from 1993 to 2003, satellite observations provide an estimate of 3.1 ± 0.7 millimeters sea level rise per year, or about an inch and a quarter over that decade. So, what is wrong with the IPCC approach of multiplying that decadal rise by ten, which would give about a one-foot rise by the year 2100?

What is wrong with it is that the Earth’s climate system does not necessarily respond linearly to external influences (in climate science, these influences are called forcings, and may be either positive, causing the climate to grow warmer, or negative, having the opposite effect). Instead, if new conditions are established that result in the trapping of more or less heat in the atmosphere, or that alter fundamental patterns of ocean flow or some other basic climate variable, the response of the climate system may be very fast and nonlinear. One well-studied example of very rapid climate change in relatively recent times is an episode of cooling, termed the “Younger Dryas”, that occurred between 12,900 and 11,500 years ago. Although the source of this cooling and subsequent reheating is debated, substantial evidence indicates that temperatures in the upper latitudes of the Northern hemisphere changed on the order of 5-10 °C within just a few decades.

In the present day, if elevated carbon dioxide concentrations produce, via the greenhouse effect, an increased surface temperature that is incompatible with the existence of either the Greenland or West Antarctic ice sheets, then we could see rapid melting of one or both sheets by the end of the 21st century. Presently, the concentration of carbon dioxide in the atmosphere is about 385 parts per million (ppm), and it is increasing by 15-20 ppm per decade. Nobody knows what level will ultimately cause one or both ice sheets to melt completely, but the Fourth IPCC report suggests 445 ppm as a final target that could be low enough to prevent catastrophic melting. That level is estimated to produce an additional warming of about 1.3 °C, which may cause only more local (though still highly impactful) disruptions. The technical and policy challenges required to fundamentally change our energy economy, in time to meet this target, are extraordinary. Hence, the urgency. We do not have a decade to sit around, carrying out business as usual, while the carbon dioxide levels inevitably make their way up to 405 ppm, or higher, by 2017.

I have described the good news, and some not-so-good news, but there is, unfortunately, also some very bad news on how we are doing these days, in the first decade of the 21st century. The IPCC report makes various future projections of temperature rise and associated climate impact in its attempt to recommend policy changes, and the different scenarios it imagines depend in part on the rate of increase of carbon dioxide emissions in the future. The differences among the IPCC scenarios essentially translate to how much political will we can muster to kick the fossil fuel habit and develop renewable energy economies of global reach. In the IPCC’s worst-case scenario, termed “A1FI”, the future is one of intensive and continued dependence on fossil fuels, leading to estimated temperature increases of up to 6.4 °C by the end of this century. Other scenarios imagine transitions to a renewable energy economy over various timescales, and depend as well on variables such as assumed population increases. The data are now in for the years 2000-2004, as analyzed in a report published by an international team in Proceedings of the National Academy of Sciences on June 12 of this year. Their analysis allows us to see which projected scenario we in fact followed during that time. The data indicate that the growth rate of carbon dioxide emissions, worldwide, increased from 1.1% per year for 1990-1999, to a staggering 3.2% per year for the period from 2000-2004. This 3.2% annual carbon dioxide emissions growth rate is even worse than the growth rate assumed in the IPCC’s A1FI worst-case scenario. The recent upturn is due primarily to increased emissions from China and other parts of the developing world. The United States, however, also has increased its emissions rate since the year 2000, and is responsible, in cumulative impact, for 30% of the total emissions since the start of the Industrial Revolution.

We are, to put it mildly, not off to a great start in this new century. The latest analysis underlines the need for urgency in the starkest possible terms. There is, quite literally, no time to lose.