Climate change is the defining issue that the world faces. Left unchallenged, climate change and extreme weather events will reshape the entire planet. However, understanding why the climate is changing is a very complicated subject with extensive interconnected natural forces and human factors dictating the severity of the crisis. Learning the fundamental science behind climate change can improve one's knowledge of the causes, sources, and solutions needed to limit runaway climate change.

The following section highlights key climate science with the latest climate change projections to enhance awareness of the issue. 

What is the global climate?
The Earth's global climate is a dynamic system that involves complex interactions between the atmosphere, land, oceans, and biosphere. The global climate is powered by incoming radiation from the Sun. The greenhouse effect manages global temperature and keeps the entire planet from experiencing sub-freezing temperatures at the equator. Positive and negative feedback loops regulate the global climate to buffer any imbalance in the system, with overall changes occurring gradually. 

What are greenhouse gases?

Greenhouse gases (GHG) are a class of molecules with unique heat-trapping properties that can absorb reflected solar radiation from the Earth and then re-emit that captured energy to its surroundings. When concentrations of GHGs increase within the atmosphere, more solar energy is captured and re-emitted, leading to atmospheric warming. Changes in atmosphere temperature alter the delicate balance of planetary regulations needed to maintain temperatures, precipitation patterns, and ocean characteristics.

Different GHGs have varying capabilities to capture radiation and cause heating of the atmosphere, referred to as its global warming potential (GWP). The global warming potential of carbon dioxide (CO2) is valued at one because CO2 is considered the base greenhouse gas that all other GHGs are compared against. The other GHG's global warming potentials are calculated and converted to create a standard impact value between all GHGs (see table below). For example, one CH4 molecule has 28 times more heating potential than one CO2 molecule; alternatively, 28 CO2 molecules are needed to equal the impact of one CH4 molecule.

GHGs Global Warming Potentials and Sources
Common GHGsFormulaGWP100Natural and Human Sources
Carbon Dioxide CO2 1 Biosphere, organic decay, fossil fuel combustion
Methane CH4 28 Organic decay, animal digestion, fossil fuel combustion
Nitrous Oxide N2O 265 Soils, oceans, farmland fertilizer, combustion
Chlorofluorocarbons CFCs 300-9,000 Industrial processes and by-products
Hydrofluorocarbons HFCs 10-10,000 Industrial processes and by-products

Sources of greenhouse gas emissions

Greenhouse gases are produced by a variety of natural and human sources. Examples of natural sources include CO2 emitted from forest fires, methane created by wetlands, and N2O from soils. Over time, these natural sources of GHGs can be removed from the atmosphere and slowly absorbed by the biosphere, land, or ocean systems. However, the addition of human sources of GHGs causes an imbalance in the natural cycling of gases out of the atmosphere, which induces atmospheric heating. Examples of human sources include fossil fuel combustion, cattle methane, artificial fertilizers, and refrigerants.

The most significant driver of climate change is from human GHG sources which far exceeds the impact from natural sources. The unmitigated release of human sources of GHGs ultimately leads to a greater effect on the atmosphere and the unravelling of the global climate system. At current GHG emission rates, global temperatures will increase by 2.4oC to 4.8oC by 2100. 

Which greenhouse gas contributes the most to climate change?

On a global scale, CO2 has the greatest overall GHG impact because of the total volume emitted and its longevity to remain within the atmosphere to induce continuous climate change. In 2016, carbon dioxide emissions from all sources added 35.22 billion metric tons to the atmosphere. To put into context, in 1916, all global sources of CO2 emitted 3.38 billion metric tons representing a rise of 942% over that period. Additionally, CO2 released today will remain in the atmosphere trapping radiation for centuries before being removed through natural processes. 

Methane is the next important GHG because of the potency of its GWP and the recent expansion of natural gas over the last 50 years. In 2016, worldwide methane emissions reached 8.55 billion metric tons. The impact from methane is severe but fortunately not long lasted, remaining in the atmosphere for approximately 12 years. Curbing methane emissions is an excellent near-term climate solution.    

Human sources of nitrous oxide originate mostly from agriculture which added 3.03 billion metric tons to the atmosphere in 2016. The lifetime of N2O is 121 years with a GWP of 265, granting this GHG with a significant impact to the climate if left unmitigated. 

Composition of GHGs in the atmosphere

What is climate change?
Climate change refers to the persistent, long-term change in the state of the global climate. Historical weather observations are averaged over 30-years to determine the typical baseline regional climate for a particular area and then compared to recent weather observations to evaluate if a change has occurred. Worldwide climate records have revealed the following key earth system changes as a result of heightened greenhouse gas emissions stimulating climate change:
  • global average surface temperature has risen by 0.87oC from 1850 to 2015
  • average air temperature in the Canadian Arctic increased by 2.3ofrom 1948 to 2016
  • sea level has increased by 21 cm due to the melting of the polar ice sheets, glaciers, and thermal expansion of ocean water 
  • multi-year Arctic sea ice has been reduced by 90% from 1979 to 2018
  • Antarctic ice sheet has lost 155 Gigatonnes of ice per year from 2006 to 2015, adding 0.48 mm to sea level rise per year

However, climate change is not uniform across the globe or in Canada. The maps below illustrate changes in regional climate characteristics from baseline measurements that have been recorded in the last decades. The map on the left depicts the annual change in temperatures in Canada from 1948 to 2016. The greatest change was observed in the west and north of Canada over that timeframe, with minimal alterations in Newfoundland. The second map displays the change in snow-water equivalent which refers to the amount of water within the snowpack during the winter months and available for the spring melt. Eastern Canada, particularly southern Ontario has recorded a decrease in snow-water equivalent of 10% per decade since 1981 to 2015. 

The impacts of climate change are affecting different regions in Canada in varying ways but significant changes have occurred and greater changes are projected to transpire. Climate change is unraveling local climate norms across the country and is imparting new seasonal weather patterns that the environment and local communities may not be able to rapidly adapt to withstand the upheaval. 

Map of Canada illustrating the change in annual temperature from 1948 to 2016     Changes in snow water equivalent in Canada

What are climate scenarios?

Climate scenarios are used to project the impact of future climate change under varying GHG concentration levels. Climate change scenarios utilize computer modelling to estimate the effect of various climate outcomes, such as sea-level rise and average global surface temperatures associated with specific GHG emission concentrations. Each scenario considers different assumptions regarding future human populations, economic activity, socio-economic activity, energy production, land use, and climate policy. Climate scenarios also illustrate the mitigation pathways required to lessen the impact of climate change.

An example of a climate scenario for Canada is displayed below that describes the Representative Concentration Pathway (RCP) 2.6 and 8.5. The light red and blue lines are individual climate models consolidated into a mean value depicted by the dark red and blue lines for each scenario. RCP 2.6 coincides with a low carbon pathway where GHG emissions peak by 2030 and hit net-zero emissions by 2050. This pathway corresponds with the Paris Agreement and will enable the rise in the average annual global temperature to hold in Canada at 2oC. The RCP 8.5 pathway represents the high emission scenario with unabated global growth in GHG emissions contributing to an annual temperature rise surpassing 7oC by 2100 above the baseline annual temperature in Canada.


High and low GHG emission climate scenarios in Canada

What is projected to happen in Peterborough?

In Peterborough, climate change is already occurring. Historical extreme weather events such as the 2004 flood and the 2018 heat wave have already impacted the community. High carbon emission climate scenario models are predicting warmer summers, shorter winters, warmer nights, and increased precipitation on average for Peterborough in the coming decades. Over the next twenty years, all climate scenarios are projecting the same outcomes until 2040, but in the following decades the greatest divergence between high and low emission pathways are modelled. If Peterborough and the rest of the world hit the goal of net-zero emissions by 2050, then Peterborough will enter into the low carbon pathway. However, if global net-zero is not achieved then significant changes to the regional climate will be guaranteed in Peterborough.  

Explore Peterborough's climate scenarios and learn more about the changes likely to unfold in the near and long-term in our community.

Considering the risk from severe weather events, some neighbourhoods in Peterborough are more vulnerable to the impacts of flooding and persistent heat waves than other areas of the city. Climate change will enhance the intensity, duration, and frequency of extreme weather which increases the potential risk to residents and the built environment from withstanding each event. Adapting Peterborough to withstand extreme weather that is projected to become a normal occurrence is important to prevent undue harm and loss of life and damage to infrastructure.  

What is 1.5oC and 2oC and why limit it?
To limit runaway climate change, global annual average temperatures need to be held at a 2oC rise but preferably 1.5oC relative to 1750s average global temperature to lessen the severe alteration to the biosphere and planetary systems. Climate scientists utilize 1750 as the baseline year to compare the changes in global temperatures against because 1750 predates the Industrial Revolution. The Industrial Revolution witnessed the introduction of coal powered steam engines that transformed manufacturing and travel that initiated the unbalanced rise of GHG emissions. Additionally, elevated global temperatures above 2oC will cause seismic changes to the biosphere and hydrosphere directly impacting humanity's ability to grow domesticated plants, such as field crops, and increase periods of drought straining global freshwater resources. Every fraction of a degree not increased greatly improves humanities ability to thrive and lessens the impact on growing food and obtaining fresh water across the planet. 
If all GHG emissions stopped immediately what would happen?

The near-term projections for the next 20 years are the same for every climate scenario, including both high and low GHG emission pathways, which all model global temperatures and sea-level rise being locked in till 2040. The guaranteed increase results from the build-up of historic greenhouse gases in the atmosphere from years past that will continue heating the atmosphere before being gradually removed through natural processes. If CO2 is significantly reduced over the next 20 years, then global temperatures will begin to stabilize and hold at around 2oC. Achieving net-zero CO2 emissions by 2050 will allow historic CO2 molecules in the atmosphere to slowly decline over the succeeding decades and centuries.   

However, sea-level rise will proceed despite the reduction in GHG emissions due to the slow inertia of oceans to respond to changes in atmospheric CO2 concentrations. The increase in sea level is a factor of ice sheet meltwater plus the gradual warming of ocean water that is leading to water volume expansion. Projections of sea-level rise range from 26 to 55 cm in a low carbon scenario and 52 to 98 cm in a high carbon scenario by 2100. Long-term sea-level rise is projected to increase by many meters in the following centuries.