The word climate has been in use for centuries. Its simplest definition is “average weather” or “prevailing weather of a region” (Concise Oxford). The origin of the word, from klima the Greek word for “inclination (slope),” usefully reminds us of climate’s connection with the sun. For the Greeks, climate was related to the angle of the sun’s rays, which produced inequalities in the number of hours of daylight in different latitudes and seasons.

In the 1960s, the word climate rather suddenly developed a negative ring to it, and the phrase climate warming began to suggest that the atmosphere was a threat to global life-support systems. (Carbon dioxide has no direct effects on human health.)

Later, in the 1980s, climate warming became climate change, indicating that many scientists realized that climate change could cause a variety of impacts such as increases in the number and severity of hurricanes, floods, droughts, bark beetle invasions, and so on.

Most scientists consider an increase in greenhouse gases (GHG), which include carbon dioxide, carbon monoxide, methane, oxides of nitrogen and water vapour, to be the main cause of the global warming trend. Carbon dioxide stays in the atmosphere for decades or centuries, so it has time to mix through both hemispheres, and up into the stratosphere. This implies that climate change must be dealt with as a global issue. A molecule of greenhouse gas over Canada may have originated anywhere in the world.

Surprisingly, the thermodynamics of climate change was understood in the late 19th century, even though measurements in the upper atmosphere were not yet possible. The Swedish Nobel Laureate, Svante Arrhenius, predicted in 1896 that the world would gradually warm as CO2 accumulated. In the 1940s, students of meteorology were taught that warming would not be detectable for many years. This proved to be wrong for two reasons: industrial and motor vehicle emissions began to increase rapidly; and for many years, it had been thought that the world’s oceans would quickly absorb the additional amounts of greenhouse gases coming from human sources. But in 1957, Roger Revelle and Hans Suess unravelled the chemistry of seawater that limited its absorptive capacity of CO2.

To detect global trends in a greenhouse gas it is necessary to select a sampling site that is free of vegetation and other small sources of carbon emissions. In the late 1950s, Charles Keeling (USA) established a CO2 monitoring station on top of Mauna Loa, a mountain peak in Hawaii, and after only several years, he had sufficient hard data to state with confidence that CO2 concentrations were rising significantly at his site! This discovery set off warning bells around the world but the actions that followed were mostly in the monitoring and research fields. (A prominent Canadian chemist argued that CO2 could not be measured with sufficient accuracy to detect a trend.)

The tipping point that triggered calls from various advocate groups for major reductions in carbon footprints occurred in 1985 when the British Antarctic Survey published a short paper in Nature that found a “hole” in the stratospheric ozone layer over Antarctica. This was the first unequivocal proof that ground-level emissions of a long-lived gas like the chlorofluorocarbons, in this case, percolate throughout the entire atmosphere. Paul Crutzen, a subsequent Nobel Laureate, called the discovery of the Antarctic hole the biggest scientific surprise in the environmental field in the 20th century! From then on, funding for global atmospheric research was given high priority by the United Nations family and other funding bodies.

In response to mounting concern about climate change, two of the UN Agencies, WMO (World Meteorological Organization) and UNEP (United Nations Environment Programme) established IPCC (Intergovernmental Panel on Climate Change) in 1988. IPCC provides climate-change information to intergovernmental and national bodies. Despite some disbelievers (see below), IPCC has generally been successful as an unbiased source of information. In 2007, IPCC jointly with Al Gore (USA) won the Nobel Peace Prize. Several Canadians are authors or reviewers of IPCC publications.

The UN Copenhagen Climate-Change Summit, also known as the Conference of Parties (COP15), a body established by the United Nations to recommend action that should be taken to stabilize concentrations of CO2 in the atmosphere. But the summit did not achieve very much, partly because the large number of participants could not possibly reach a consensus although the conference must have contributed significantly to the world's carbon footprint. Nevertheless, the summit did produce a closing statement, the Copenhagen Accord, which is available on the Internet.

Some climate change effects are already detectable in Canada including: increased melting of glaciers; warmer temperatures, particularly in the arctic; thinning of sea ice in the Arctic Ocean and the increasing percentage of open water in late summer; slow northward and upward movements of ecosystems and endangered species; increasing length of the growing season for agricultural crops; and bark-beetle damage to forests. The melting of the Arctic Ocean has brought immediacy to the Canadian public that the issue is very real.

The Canadian scientific community has important work to undertake in the coming decades. More needs to be done on the concept of dangerous climate change, which has been loosely defined in UN documents as a further increase in global mean temperature of 2° C. But how was this value derived? A determination needs to be made whether an irreversible trend is about to begin and continue over the next hundred or thousand years and if so, what are early warning indicators. Also collaboration needs to be improved between economists and themselves, perhaps with the establishment of an institute where the two disciplines can work together. Finally, scientists need to challenge climate change misinformation spread by skeptics. These people are confusing the public, and are having harmful effects on the development of public policy. Perhaps a national committee should be created to challenge these views.

Canada has a skilled cadre of climate scientists in our universities and government laboratories. But is the government listening?