Science

Weather and Climate

Weather itself is a short term, highly localized event. Disturbances and atmospheric eddies that move moisture and heat across the earth's surface, lasting only for a few seconds to several days, are called weather events. An afternoon thunderstorm or a typhoon is an example of such an event. Climate events, on the other hand, arise out of long-term, large-scale changes that span weeks to decades, a few tens to thousands of kilometers. The El Niño phenomenon that lasts for about a year, every 2 to 5 years, spanning the Pacific and other regions, is an example of a climate event.

Climate Change

Changes in our climate have been occuring naturally. Ice core data have shown that the surface temperatures for the past 420,000 years have been following a steady rhythm of warming and cooling, suggesting that climate is affected by natural forcings and feedbacks.The global temperature record of the last 420,000 years shows that the amplitude of warm and cold (interglacial and ice age) events does not go beyond 8 °C.

From this same temperature plot, we can see that we are now in an interglacial (i.e. warm) period. The historical pattern seems to suggest that the planet is bound to slide down to the next ice age in a matter of several thousand years from now. Recent temperature records and climate modeling projects indicate a radical departure from this pattern.

Human fingerprint

Most of the temperature swings in the ice core record have been attributed to changes in astronomical factors such as the geometry of earth's orbit, its inclined axis, and the like. These shifts generally occur at a frequency of several thousands of years.

IIt was only at the time of Swedish chemist Arrhenius (at the turn of the 20th century) when people realized that climate itself could likewise be affected by the chemical composition of the atmosphere. Arrhenius simply asked what would happen if carbon dioxide in the atmosphere were doubled. His calculations, however rough at that time, pointed to a warmer planet due to this chemical change.

From then on, it was only a matter of time before science realized the importance of a handful of gases in the atmosphere that are able to trap the outgoing longwave radiation of the earth, thus supplementing the warmth delivered by the sun. The greenhouse effect is made possible by the presence of trace amounts of water vapor, carbon dioxide, methane, nitrous oxide, and others.

Going back to the ice core data, we find a striking correlation between global surface temperatures and atmospheric CO₂ concentrations. While a correlation here does not necessarily determine causality, i.e. whether CO₂ variations cause temperature changes and vice versa, we note that the observed present level of CO₂ is unprecedented in the last 420,000 years. (The IPCC Third Assessment Report also states that this present level is likely unprecedented in the last 20 million years).

According to the mainstream scientific prognosis, this sudden step in CO₂ (it is sudden relative to the historical trend) is likely to lead to sudden temperature increases that range from 1.4 to 5.8 °C. This projected leap (in only a century's time) is almost comparable to the amplitude of the temperature changes in the last 420,000 years.

Looking at the atmospheric CO₂ concentrations in the past century, we find that the rapid increase in global atmospheric CO₂ concentration has been observed at the onset of the industrial revolution (late 1800s) when fossil fuels became widely used to power industries in the Northern Hemisphere.

The issue of human accountability in the problem of climate change is one of the most contentious. While the majority scientific opinion would acknowledge the fact that global temperatures are indeed on the rise, there are some who would question the mainstream tendency to link the warming to human activities that generate greenhouse gases (GHGs) into the atmosphere.

The most recent scientific assessment is clear on this issue of human accountability:

• "The warming over the past 100 years is very unlikely to be due to internal variability alone."
• "Detection and attribution studies consistently find evidence for an anthropogenic signal in the climate record of the last 35 to 50 years."
• "Simulations of the response to natural forcings alone (i.e. the reponse to variability in solar irradiance and volcanic eruptions) do not explain the warming in the second half of the 20th century."
• "The warming over the last 50 years due to anthropogenic greenhouse gases can be identified despite uncertainties in forcing due to anthropogenic sulphate aerosol and natural factors."

Global scope

The increase in CO₂ levels in the atmosphere is not locally confined to certain areas of the planet. Measurements of the background concentration of CO₂ at remote sites such as the Mauna Loa mountain in Hawaii indicate that CO₂ is everywhere increasing progressively.

The wavy patterns in this plot are the annual variation of concentrations due to the CO₂ uptake by growing plants during the northern hemisphere springtime.

The global extent of CO₂ is due mainly to the long residence time of this gas in the atmosphere, lasting from years to decades.

Compounded impact

It is sometimes argued that CO₂ is a minor trace gas in the atmosphere and that its greenhouse warming capacity (i.e. radiative forcing) is miniscule compared to that of water vapor. What is however neglected in these arguments are the positive feedback mechanisms that can compound the initial disturbance of rising CO₂ levels in the atmosphere.

One such feedback mechanism is the ice-albedo effect in which melting ice reduces the reflectivity (or albedo) of the earth's surface thus absorbing more of the sun's warming radiation. Greater absorption will lead to increasing surface temperatures.

Another positive feedback mechanism concerns the ocean-CO₂ effect in which warming oceans will naturally release more CO₂ from the water into the atmosphere. This phenomenon is readily observed in soda drinks that lose their fizz (i.e. carbonation) when warmed. More CO₂ in the atmosphere will in turn warm the ocean even further, leading to greater amounts of CO₂ realeased from the ocean into the air.

Climate change due to increasing CO₂ as well as rapid climate change is therefore a possibility due to such feedback effects.

Global response: Concern ...

Concerned by the mounting evidence that human activities have the potential to change the climate system and that this change is posing a threat to our survival, the global community through the World Meteorological Organization (WMO) and United Nations Environmental Programme (UNEP) formed the Intergovernmental Panel on Climate Change (IPCC) in 1988. The IPCC was tasked to assess the scientific, technical and socio-economic information on climate change and provide a balanced report on the issue.

... and skepticism

Despite these assessments, skeptics of the climate change issue say that it is needlessly alarmist. They argue that the methodologies for determining the existence of climate change are scientifically flawed and that the climate is not changing. Neither do CO₂ emissions affect the state of the climate.

Others agree that there is climate change but the cost of immediately reducing CO₂ emissions is detrimental to the growth of economies dependent on fossil fuels. They also argue that the targets and timetables like the ones set in the Kyoto Protocol are unrealistic. They instead push for voluntary and technology-based methods for reducing emissions.

Other groups claim that CO₂ emissions from fossil fuel combustion are actually beneficial and should not be reduced.

As more evidence on the real state of the climate system is gathered and models that predict future climate scenarios are developed and improved, the mainstream scientific opinion suggests that it is prudent to take precautionary actions now instead of finding out much later that it is already too late to save our planet.