Climate Change Lectures - Week 1

Weather vs Climate

• Walking a dog, the dog meandering around is weather while your straight path is the climate 

• Weather tells you what clothes to wear each day, climate tells you what you have in your closet 

Weather

• The instantaneous state of atmospheric conditions for a given place at a given time 

• Weather is always changing 

What is climate?

• The average set of atmospheric conditions for a given region 

  • Just like weather climate is ever changing but usually this occurs slowly 

Examples of climate types

• Arctic 

• Continental 

• Tropical 

Effects of Latitude and Elevation on Climate 

• These effects are dominant

• In the winter, due to atmospheric conditions we see temperatures descend all the way across Canada.

• In coastal areas we don't have quite as cold winter temperatures. 

  • In the summer coastal areas have a significant cooling affect 

Climate Normals 

• Typically climate values are presented as normals averaged over a 30-year period 

• No quantitative reason to use 30 years 

  • Longer time periods are better for understanding variability and trends  

Climate Anomalies

• Climate anomalies refer to deviations from a climate normal 

  • Anomaly = (observed value) - (climate Normal for the same unit of time for a longer or different time period) 

Relation of Anomalies

• Anomalies can be related across long distances 

• However there is more correlation the closer they are 

Climate Change

• Refers to modification of the mean or distributional characteristics of climate in a region for a specific period 

• Can be caused by natural or anthropogenic (human) processes 

• Relevance of climate change is dependent on timescale and metric of interest 

Change in frequency of the coldest days 

• In areas in Canada (northwestern) we've seen a huge decrease in the numbers of coldest days, but we haven't seen the same increase of numbers of really hot days 

Global Climate Change 

• Refers to the modification of the mean or distributional characteristics of global climate for a specified period

• Can be due to natural or anthropogenic (human caused) processes 

What do extended periods of global climate change require?

• Extended periods of global climate change requires a radiative imbalance 

• Imbalance between energy entering and leaving Earth’s lower atmosphere

Terminology (Global Warming vs Climate Change)

• There have been many periods of global climate change in the past 

• There have been relatively fewer periods of global warming 

Specific Heat

• Specific heat is the amount of energy needed to raise temperature 

• Higher specific heat means its harder to warm or cool 

Thermal inertia

• Measure of thermal mass

• Responsiveness to temperature changes 

Feedbacks

• Feedbacks are processes initiated by an external change to a system that alters the systems response to the initial change

Positive Feedbacks

• Positive feedbacks amplify an initial perturbation 

  • Initial warming leading to processes that trigger more warming 

Negative feedbacks

• Negative feedbacks diminish an initial perturbation 

  • Initial warming leading to processes that trigger less warming

Examples of Climate Feedbacks 

• Snow/ice albedo feedback 

  • Positive: Warming > less snow > warmer > less snow 

• CO2 - Ocean warming feedback 

  • Positive: CO2 > ocean warming > less CO2 uptake in warmer oceans > ocean warming 

• Water vapour feedback 

  • Positive: Warming > more atmospheric moisture > more warming 

• Cloud - warming feedbacks 

  • Negative: Warming > more atmospheric moisture > more clouds > more shortwave reflectance > less warming 

Fast Feedbacks

• Feedbacks that occur relatively quickly (days - months - years) 

  • Climate system components with fast response times

Slow Feedbacks

• Feedbacks that occur relatively slow (years - decades - centuries) 

  • Climate system components with slow response time