Lecture 5: Emissions and climate mitigation

Climate mitigation

Consists of actions to limit the magnitude or rate of long-term global warming and its related effects. Mitigation may be achieved by reducing carbon sources or increasing carbon sinks.

We have to understand the current emissions and what is producing them and by what sector and country. Then we can focus on how we might mitigate these emissions

Global fossil CO2 emissions

38.1 Gt CO2 in 2025 (1.1% increase). The graph has a positive linear relationship.

Top fossil CO2 emitters

China (32%), USA (13%), India (8%), EU (6%), Russia (5%) and Japan (2%) are the top emitters in 2024.

Historical cumulative fossil CO2 emissions

USA (440 Gt CO2), EU (300 Gt CO2) and China (280 Gt CO2) have the highest historical emissions.

Top emitters fossil CO2 emissions per capita

USA (14.2 tonnes/person), Russia (12.3 tonnes/person), China (8.7 tonnes/person) are top emitters per capita in 2024.

Greenhouse Gas Emissions

• Mainly carbon dioxide (CO2) and methane (CH4)

• Fluorinated gases (F-gases) also have a large potent effect on climate

GHG emissions by sector (globally)

• Electricity and heat (17 billion t), transport (8.5 billion t), manufacturing and construction/industry (6 billion t), agriculture and land use (6 billion t) are the biggest emitting sectors

Sustainable cities and communities (SDG 11)

• 4.2 billion people (55% of global population) lives in cities

  • urban population is expected to reach 6.5 billion.

• Cities occupy just 3% of the Earth’s land

  • 70% percent of carbon emissions.

• 828 million people are estimated to live in slums, and the number is rising

• In 1990, there were 10 cities with 10 million people or more; by 2014, the number of mega-cities rose to 28, and was expected to reach 33 by 2018

  • in the future, 9 out of 10 mega-cities will be in the developing world.

• 90% of urban expansion will be in the developing world in future decades

• The economic role of cities is significant

  • they generate about 80 percent of the global GDP

Urban emissions

• Top 25 cities accounted for 52% of the total urban GHG emissions

  • cities in Europe, Australia, and US had significantly higher per capita emissions than developing cities

• Stationary energy and transportation were the two main sources of emissions

• 30 of the 42 cities decreased the annual GHG emissions over the study period

  • in several cities there was an increase in emissions

  • 113 out of the 167 set varying types of GHG emission reduction targets

  • 40 have set carbon neutrality goals

Fossil CO2 emissions by source

• Coal (41%/15.9 Gt CO2), oil (32%/12.6 Gt CO2), gas (21%/8.1 Gt CO2), cement (4%/1.5 Gt CO2) in 2025

Australia top emissions per sector and type

• Agriculture (215 million t), electricity and heat (199 million t), transport (99 million t) are the top emitting industries in Australia

• Oil (150 million t), coal (148 million t) and gas (75 million t) are the top emitting sources

Scope 1, 2 and 3 emissions

• Scope 1

  • direct emissions

  • those that a company causes by operating the things that it owns or controls

  • e.g. running machinery to make products, driving vehicles, or just heating buildings and powering computers

• Scope 2

  • indirect emissions

  • created by the production of the energy that an organization buys

  • e.g. installing solar panels or sourcing renewable energy rather than using electricity generated using fossil fuels would cut a company’s Scope 2 emissions

• Scope 3

  • indirect emissions

  • those not produced by the company itself

  • cover those produced by customers using the company’s products or those produced by suppliers making products that the company uses

• Scope 4

  • avoided emissions

Mitigation pathways

• multiple scenarios with a range of technological and behavioural options, with different characteristics and implications for sustainable development, that are consistent with different levels of mitigation

• IPCC SR15 looked at the mitigation required to reach 1.5 C

• IPCC AR6 WGIII looked at 6-8 different scenarios to reach different degrees of global warming

Mitigation required for 1.5C

• Limiting warming to 1.5°C means net zero CO2 emissions globally around 2050 and concurrent deep reductions in emissions of non-CO2 forcers, particularly methane (high confidence)

• The share of primary energy from renewables increases while coal usage decreases across pathways limiting warming to 1.5°C with no or limited overshoot (high confidence). - reduction in coal and increased renewable energy

• 1.5°C pathways with no or limited overshoot include a rapid decline in the carbon intensity of electricity and an increase in electrification of energy end use (high confidence). - switch to electric transport options - EVs

• Transitions in global and regional land use are found in all pathways limiting global warming to 1.5°C with no or limited overshoot, but their scale depends on the pursued mitigation portfolio (high confidence). – reduced deforestation

• Demand-side measures are key elements of 1.5°C pathways. Lifestyle choices lowering energy demand and the land- and GHG-intensity of food consumption can further support achievement of food, reduced air-travel