“Keep 1.5 alive” was the demand heard from many demonstrators at the COP26 climate conference in Glasgow in November 2021, echoing United Nations Secretary-General António Guterres’s opening remarks in which he called on the delegates to “keep 1.5 degrees Celsius alive” – limiting global temperature rise this century to 1.5 degrees Celsius, compared to pre-industrial levels.

Achieving that target means reducing global greenhouse gas emissions to zero by 2050. Strange as it may seem, reducing our emissions sources to zero does not mean we must stop using carbon-intensive fuels by 2050. However, it does mean that our total emissions must be zero.

What’s the difference?

A jurisdiction’s total emissions are the sum of its emissions sources and emissions sinks. Emissions sources are activities that emit greenhouse gases, including transportation, power generation, buildings, industry and agriculture. Emissions sinks are entities that capture and store carbon and are grouped into either nature-based solutions (notably biological, forests, croplands and wetlands) or technical solutions (including direct air capture and geological storage, and carbon mineralization).

By 2050, every jurisdiction will be in one of three emissions states. If its emissions sources are in balance with its sinks, it will have reached net zero. It will be net negative if the emissions sources are less than the sinks. If its emissions sources exceed its emissions sinks, it will be net positive and will need to find other sinks to become net zero – for example, by purchasing sinks from a net-negative jurisdiction.

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Canada and Nova Scotia

In late 2020, the federal government committed Canada to achieving net-zero emissions by 2050. Part of its net-zero plan includes a redefinition of how nature-based emissions are calculated. Prior to 2020, they were excluded from emissions sinks. However, starting with the 2020 National Inventory Report, to be released in May, they will be included, resulting in a decrease in Canada’s emissions by an additional 25 megatonnes (Mt).

Some provinces and territories also have some form of net-zero legislation. Nova Scotia has two bills (from 2019 and 2021), both stating, “Greenhouse gas emissions in the Province are by 2050, at net zero, by balancing greenhouse gas emissions with greenhouse gas removals and other offsetting measures.”

Since global warming does not afford us the luxury of waiting until 2049 to act on net zero, we decided to conduct an analysis of Nova Scotia’s existing nature-based solutions to estimate a baseline for the province’s sinks. This gives the province an upper limit on its emissions sources, and time to take steps to maintain and improve its existing sinks and develop new ones.

Our analysis indicates that in 2019, Nova Scotia’s nature-based solutions totaled -11.5 Mt. The forest and wetland sink fluxes (or changes in CO₂ emission) were -9.7 Mt and -1.9 Mt, respectively, making them net-emissions sinks. However, croplands were a net-emissions source, emitting 0.1 Mt.

Between 2005 and 2019, Nova Scotia experienced a 30 per cent reduction in its emissions sources. However, when compared to its 2019 emissions sinks, the province’s total emissions were still 4.7 Mt, making it net positive.

Nova Scotia has committed to reducing its emissions by 53 per cent below 2005 levels by 2030, or about 10.9 Mt. If the 2019 emissions sinks remain unchanged in 2030, Nova Scotia’s total emissions would be about -0.6 Mt, making the province net negative (Figure 1). If the sinks and the sources remain constant between 2030 and 2050, Nova Scotia would still be net negative in 2050, with total emissions of -0.6 Mt.

We have also considered the situation in which the province’s nature-based solutions increase between now and 2050, with forest sinks continuing to increase in strength by about 0.32 Mt every five years; improved cropland practices fully implemented by 2050, causing Nova Scotia’s soil organic carbon to reach the levels found in the U.S. for cover crops, improved crop rotation and no-till farming; wetland sequestration remaining constant and wetland restoration increasing CO₂ removal by four per cent of the baseline value every decade.

The consequences of these changes will see an increase in sink strength, with forests, wetlands and croplands removing -11.6 Mt, -2.1 Mt and -0.2 Mt, respectively, by 2050, resulting in a total sink flux of -13.9 Mt. Assuming the 2030 sources remain unchanged in 2050, the province’s total emissions would be -3.0 Mt, making it net-negative (Figure 2).

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Both the constant and increasing sink flux examples see Nova Scotia becoming net negative in 2050. However, the province’s nature-based sinks are prone to the effects of global warming, which could change this picture.

In forests, this includes droughts (which have occurred in the province during six of the last 10 years); fires (wildfires have been reported in the province every year for the past five years); pests (the province is affected by the spruce beetle, which is endemic, and the sap-sucking hemlock woolly adelgid, which damages hemlock and spruce trees); extreme weather events such as hurricanes and post-tropical cyclones (which threaten to damage and uproot shallow-rooted trees, including commercial populations of spruce, balsam fir and red maple); and human-induced events such as forest clearing.

Diked croplands in the Annapolis Valley are at risk from saltwater intrusion because of rising sea levels; low-lying croplands are vulnerable to the expected increase in annual precipitation and more intense rainfalls; and soils are at risk of losing some of their water-holding capacity. Threats to wetlands include coastal erosion and flooding from rising sea levels.

As an example (Figure 3), we considered the situation in which the sinks decline by 10 per cent by 2050, compared with their 2019 levels, resulting in an emissions sink strength of -7.9 Mt. If 2050 sources remain unchanged from 2030, the province’s total emissions would be +3.0 Mt in 2050, making it net positive.

Technological systems

If natural sink strengths decline because of global warming and the province enters into, or remains in, a net-positive state, it will be necessary to employ technological systems that extract carbon from the atmosphere and then either sequester it or find another use for it.

Atlantic Canada, including Nova Scotia, has numerous sedimentary basins with large reservoirs (Figure 4) that might make them ideal candidates for carbon sequestration.

However, technological solutions, while falling in price, require energy to operate. One estimate suggests that direct air capture could decrease the costs of meeting international climate targets, but would require one-quarter of the world’s electricity by 2100.

Policy proposals

In November 2021, we made submissions to the Nova Scotia government recommending changes to its net-zero legislation, including the following:

1. Conduct a complete and accurate biannual assessment of the province’s greenhouse-gas fluxes of the biological sinks.
2. Measure, report and verify the threats to Nova Scotia’s biological sinks and conduct a survey of the potential solutions to reducing the threats and vulnerabilities of the sinks.
3. Continue to reduce our emissions sources now and after 2050 to reduce the need to use technological systems or purchase sink credits.
4. Introduce tax credits for carbon captured in natural sinks to promote their protection and expansion and to increase their carbon-capture ability.
5. Research and, if possible, develop geological storage capacity as an alternative to biological sinks at risk from extreme climate events.

These recommendations were intended to continue reducing our existing emissions sources and help maintain and improve Nova Scotia’s nature-based solutions while preparing for the effects of global warming by developing the province’s geological storage. However, the provincial government ignored them.

At the end of COP26, Guterres said that achieving the 1.5 degree Celsius target this century was not dead, but “on life support.” Choosing to ignore nature-based solutions will do nothing to help revive it.