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Friday, Oct 19, 2018

Climate Change - Frequently Asked Questions

Climate Change FAQ

Recognizing the risks of climate change to our natural and built environment, Associated Engineering now offers expertise in assessing climate change impacts on all our projects.

What is climate? 

Climate is the statistics of weather.  It can be measured in many ways, from average summer temperature to the long-term return frequency of strong precipitation events.  Because many individual weather events are combined to calculate weather statistics, long-term, average climate may be quite different than individual extreme weather events.  For example, the climate in Yellowknife is cold by Canadian standards (even though Yellowknife can get quite hot during some summer days), whereas the climate in Kelowna is relatively warm (even though Kelowna can get quite cold during some winter nights).

What is climate variability?

Climate variability is the periodic variability of weather statistics.  Climate variability is a natural process that can be separated into different ‘modes’.  An important climate variability mode is the 2-7 year El Niño/La Niña cycle, which impacts the likelihood of Canadian summer forest fire disasters.  

Another important climate variability mode is the 40-60 year Pacific Decadal Oscillation, which regulates Western Canada water supply.  Importantly, variability modes are periodic and so oscillate pendulum-like around long-term average climate conditions.

What is climate change?

In contrast, climate change is a long-term, permanent change in weather statistics. In other words, the entire pendulum shifts to an entirely new location!  Climate change can be driven by a range of factors.  

We are now experiencing rapid and unprecedented climate change that is driven by human activities, particularly the extraction and combustion of geologic reservoirs of fossil coal, oil, and natural gas. The product of this combustion is carbon dioxide, a heat-trapping gas when accumulated in the atmosphere. Unlike climate variability, climate change will not reverse direction (at least for many centuries).

How do we separate climate change from climate variability?

Since climate variability and climate change both occur at the same time, the signal to noise ratio (SNR) concept is an important concept in climate science: climate variability represents the noise, while climate change represents the signal.  Separating the two can sometimes be done visually. For example, average Canadian summer temperature changes show a clear trend towards higher temperatures despite large interannual variability.

Temperature change

Observed Canadian winter temperature change 1948-1949 to 2016-2017, from Environment and Climate Change Canada meteorological station data.  Jumps from year-to-year highlight natural variability, while the red best-fit line represents the climate change signal, which can also be easily seen from the blue time series.

However, more rigorous approaches, originally applied by electrical engineers, can also be used.  SNR analyses benefit from extensive observations (e.g. 60 years of Canadian winter temperature records) so that climate variability (for example, a particularly strong El Niño) is not accidentally mistaken for a climate change signal.  

Today, SNR analyses clearly show emergence of a climate change signal across almost all climate measures.  Climate models indicate that this trend will accelerate, making climate risk assessments and climate adaptation decisions a new normal for 21st century engineers.