Here are some more questions about the changes that are happening to the climate:
Q1: Water vapour
Water vapour is the most abundant greenhouse gas in the atmosphere, yet other greenhouse gases (such as carbon dioxide and methane) are often portrayed as the main drivers of climate change. Why is that?
Answer:
When compared to other greenhouse gases (GHG), water vapour stays in the atmosphere for a much shorter period of time. Water vapour will generally stay in the atmosphere for days (before precipitating out) while other greenhouse gases, such as carbon dioxide or methane, will stay in the atmosphere for years to centuries thus contributing to warming for much longer (1).
Based on the data collected since the late 1970s, it is believed that the Sun’s radiative forcing (which is approximately 0.09 W/m2) is much less than that of greenhouse gases (which is approximately 0.40 W/m2) (2).
In the past, carbon dioxide levels rose after temperatures rose. Does this indicate that rising carbon dioxide levels are an effect of, and not a cause of, rising temperatures?
Answer:
Comparing the natural progression of ice ages to the observed increase in the global average temperature since industrialization is not a just comparison. These two processes were triggered by two very different drivers: ice ages are driven by natural triggers, while recent warming is not.
Is there a “consensus” in the science community on climate change?
Answer:
The average global temperature at the Earth’s surface has warmed by about 0.6°C since the late 19th Century. The consensus of scientific opinion is that the Earth’s climate is being affected by human activity. Thus, despite claims made by some groups that there is not good evidence that the Earth's climate is being affected by human activities, the scientific community overwhelmingly agrees that such evidence is clear, reliable and persuasive.
The Intergovernmental Panel on Climate Change (IPCC) states (2007), “Most of the observed increase in global average temperatures since the mid-20th century is very likely (>90%) due to the observed increase in anthropogenic greenhouse gas concentrations.”
How do scientists know human activities are the cause?
Answer:
A number of factors clearly point to the role of human activities as the primary source of increases in greenhouse gas (GHG) concentrations in the atmosphere. The rapid rise in GHG concentrations during the past century is consistent with trends in human emissions.
The relative abundance of CO2 molecules in the atmosphere containing the radioactive carbon 14 atom is declining. This is consistent with increased concentrations from the burning of coal, oil and natural gas, all of which contain ‘old’ carbon without carbon 14. Changes in the proportion of carbon 13 and carbon 12 in oceans are also consistent with human emissions.
Couldn’t this be part of the natural warming and cooling of our planet?
Answer:
The Earth’s climate warms and cools naturally. The natural factors that effect these changes in climate occur over thousands, if not tens of thousands of years. The current change in climate has largely taken place in the last century, particularly in the last few decades.
Global temperatures indicate that the 20th century was very likely the warmest century of at least the past millennium, and the 1990’s were likely the warmest decade of this period. Although natural changes may contribute to the phenomenon, they do not match the very accelerated rate at which the Earth is warming.
Scientists predict that the Earth will warm only a few degrees. Why should we be concerned about such a small change?
Answer:
Scientists project a 1.4—5.8ºC rise in global average surface temperature (GAST) over the next century. While this may not seem large, it is.
The difference between present-day GAST and that of the last glaciation (18,000 years ago) is only about 5ºC. This change was enough to melt ice sheets off continents and cause huge changes to ecosystems. A small change in GAST has a big impact on life on Earth.
Humans contribute a very small amount of carbon to the atmosphere compared to natural processes. How can it have such a huge impact?
Answer:
Our planet has a natural cycle that moves huge amounts of carbon— 200 billion tonnes—into and out of the atmosphere every year. When the cycle is balanced, atmospheric carbon dioxide (CO2) levels remain relatively stable.
Careful measurements over the past few decades have confirmed that CO2 in the atmosphere is increasing. Human activities are adding about 7 billion tonnes of carbon into the armosphere every year, which is only about 3–4% of the amount exchanged annually. This small addition is enough to upset the fine balance, surpassing nature’s ability to absorb carbon. The oceans and land are currently absorbing half our emissions, but the rest remains in the atmosphere for at least another 100 years.
Basic physics tells us that greenhouse gases (GHG) trap the Earth’s heat and cause warming. But the Earth’s climate is very complex, involving interactions between the air, land and oceans.
Scientists use computer models, Global Circulation Models (GCM), to project climate changes associated with the increased concentration of GHGs. Present models are able to simulate our current climate and reproduce variations in past climate. With improvements in computing power, these models continue to become more refined and accurate.
How can we talk about climate change over the next 100 years when we can’t be sure of tomorrow’s weather?
Answer:
Weather and climate are different. The methods used to forecast changes in weather and climate differ as well.
Climate can be thought of as average weather, including weather’s variability over long time periods. Natural changes in climate happen over the course of decades, centuries and many millennia. Global Circulation Models (GCM) are able to account for the many factors that influence climate over long periods, such as changes in the sun’s energy and the level of greenhouse gases (GHG) in the atmosphere. These models tell us what the average weather is likely to be but are not able to identify specific weather events.
Watch this 1-min video explaining Trend & variation:
Are the temperature records affected by the urban heat island effect?
Answer:
As population centers grow in size, they also have a corresponding increase in average temperature. Scientists refer to this phenomenon as the “urban heat island effect” (UHIE).
Extensive research shows the UHIE can account for a small amount (~0.05ºC at most) of the global warming observed over the past century. In fact, trends from rural and urban stations are very similar. Furthermore, the ocean and borehole records, which are not affected at all by the UHIE, show similar amounts of warming over the last century.
I hear scientists talk about uncertainty. Does this mean they are uncertain that climate change is real or that it is due to human activity?
Answer:
Scientists are in overwhelming agreement that humans are causing climate change. The uncertainty lies in quantifying the exact amount of influence.
Uncertainty is expected in all scientific experiments and models. Having uncertainty does not make scientific results useless. It is the magnitude of uncertainty that is important. This term has been incorrectly interpreted and intentionally misused by some skeptics.
Are the recent extreme weather events caused by climate change?
Answer:
Given our knowledge of global warming and our changing climate, we can expect more extreme weather events and side-effects, including flooding and storms. But the attribution of any particular extreme weather event to climate change remains beyond the current limits of scientific capability.
