Climate change represents one of the most serious challenges that society is facing in this century. It is important for humanity to limit its interference with the climate system by profoundly modifying activities such as burning fossil fuels and deforestation, a change that amounts to having a second industrial revolution. For this purpose, it is necessary to communicate to the public and to decision makers in government, with clarity and objectivity, the causes, consequences and solutions to climate change, so that society implements without much delay the necessary actions to confront the challenge.
Although there remain uncertainties in our understanding of the science of climate change, such as those connected with the feedback effects of clouds and aerosols, the scientific foundation of the problem is very well established, and is based to a large extent on laws of physics and chemistry discovered at the beginning of the 20th century. The average temperature of the Earth's surface has increased so far by about 0.8 degrees Celsius, and there is a very clear consensus among experts that this increment is a consequence of human activities. Furthermore, it is clear that the risk of causing changes in the climate system with potentially catastrophic consequences increases rapidly if the average surface temperature of the planet increases three or more degrees Celsius.
Extreme weather events such as heat waves, floods and droughts have occurred with increased frequency in recent years. An important question is whether there is any connection between such events and climate change. Until a few years ago the scientific community stated that there was no statistical evidence to give a positive answer to the question. However, more recently, scientists have published a series of papers indicating that there is indeed a connection. The confusion was due in good measure to the way the question was asked: there is indeed little, if any direct evidence that specific extreme events are caused by climate change; on the other hand, evidence is accumulating that the intensity of many such events has increased recently, and that the probability that this increment is a consequence of climate change is indeed significant. For example, a recent report based on satellite measurements of surface temperatures in the northern hemisphere indicates that the probability of occurrence of heat waves, defined as those with temperature departures from the 1950’s mean reaching three standard deviations, has increased tens of times in the last 50 years; the report attributes the increment to the change in composition of the atmosphere, which is in turn caused by human activities. Yet another paper that appeared in the literature recently examined six specific extreme events that took place in 2011, including the Texas and northern Mexico drought that had sizeable economic consequences, the conclusion being that five of the six events were connected with climate change; the exception, namely a flood in Thailand that also had important economic consequences, was not connected with climate change, as the amount of rain in the affected region was not really unusual; the problem was caused by changes in river basins carried out by society. Yet another example of an extreme weather event was Hurricane Sandy, which had devastating consequences in the East Coast of the United States in 2012. Here again, experts did not try to establish that the hurricane was caused by climate change, but rather investigated if the intensity and other characteristics of the storm were affected by climate change, and concluded that there was indeed a very likely connection. Among other factors, the surface temperature of the oceans affects quite substantially the power of a hurricane. The overall conclusion is that climate change poses a threat not only to future generations towards the end of the century, but also to our children and to our own generation.
Experts agree as well that a solution to the climate change challenge is indeed feasible, although by no means easy, and it requires implementing many actions simultaneously. These include using energy much more efficiently in the transportation, construction and industrial sectors, as well as reducing emissions of carbon dioxide caused by burning fossil fuels both by utilizing renewable energy sources such as wind, geothermal and biomass, and possibly also by developing and using safer nuclear energy power plants. A number of leading environmental economists estimate the cost of such measures as something between -1% and 3% of global GDP, the most likely number being between 1 and 2% per year. It is clear that the cost of not taking the necessary measures is larger, considering the damage caused by droughts, floods, forest fires, intense hurricanes, etc. In addition, it appears that the countries that will be most affected are those with least resources, which makes it imperative for the entire planet to seek an equitable solution to the problem.
Furthermore, given the uncertainties in our understanding of climate change science and likely future emissions of greenhouse gases, one cannot rule out temperature increments of more that 4 or 5 degrees Celsius towards the end of the century. The associated risk is unacceptable for society. It is important to clarify, though, that science itself does not tell us what to do; it can only inform us what is likely to happen as a consequence of our activities. It is, thus, an ethical responsibility for us and for society as a whole to respond to the messages conveyed by climate change science, in order to insure that the human population can enjoy now and in the future a quality of life at least as good as the one many of us have today.