Currently, fossil fuels (coal, oil and natural gas) provide the majority of the world’s energy supply. Renewable energy sources (like solar, wind, hydro, biomass, and geothermal) make up about 14% of global primary energy supply, and nuclear energy supplies about 5% (IEA 2019). This energy is then utilized by four sectors:
- Industrial sector (which includes agricultural processes, chemicals, iron/steel, mining, construction, forestry, etc.)
- Residential sector (including household heating, cooling, lighting, consumer products, etc.)
- Commercial sector (including commercial heating, cooling, lighting, refrigeration, computers of offices, stores, hospitals, schools, etc.)
- Transportation sector (all road, rail, air, water and pipeline needs)
World Greenhouse Gas Emissions in 2016 (Sector | End Use | Gas)
The energy system has greatly improved the standard of living for many humans, but the accumulation of carbon dioxide and other greenhouse gas emissions from energy production (burning of fossil fuels) are primarily responsible for climate change. If left unaddressed, climate change will result in catastrophic disruptions to all life on Earth, including humans (IPCC 2014). To minimize the impact of the energy system on the climate for the long haul, it will be necessary to provide the energy services in each of these sectors with clean energy sources, all while maintaining and equitably improving quality of life.
Reaching a clean energy system that eliminates greenhouse gas emissions is a challenge that requires support and action from all sectors of society. The global energy system has to go from over 80% fossil energy today with about 33 gigatons of carbon dioxide equivalent (GtCO2e) (IEA 2019) entering the atmosphere each year to zero emissions. The longer it takes for global emissions to peak, the steeper the annual decline has to be from that point if desired temperature goals are to be met.
Energy expert Vaclav Smil notes that past energy transitions take multiple decades (or longer) to achieve. Accelerating the timeline for an energy transition that limits average global warming to below 2ºC / 3.6ºF will take a focused effort and considerable political will—a transformation of the global energy system. Efficiency, consumer choice, advances in technologies, and equitable energy services for underserved populations are all at play. At our current rates of emissions, we’ll exceed the carbon budget for 1.5°C in less than a decade, and the 2°C carbon budget in 20-25 years. Limiting global warming to either a 1.5ºC or 2ºC increase will be incredibly ambitious, but necessary to avoid the catastrophic impacts of climate change on a business-as-usual pathway. While the difference between a 1.5ºC vs. a 2ºC increase sounds small, the change in impacts is significant for natural and human systems. Food production, human health, and various vital ecosystems (notably coral reefs) will be much less impacted and better able to adapt in a 1.5ºC future (IPCC 1.5ºC Special Report 2018).
Energy Efficiency Improvements
Improving energy efficiency reduces how much energy is needed to achieve the same amount of work. For example, a more energy efficient home will provide the same quality of services to inhabitants in terms of hot water, heating, cooling, and lighting but using a smaller amount of energy. While clean energy is growing at an exponential rate, meeting global energy demands with clean energy in the timeframe needed to limit global warming to below 2ºC requires a reduction in overall energy needs (IPCC 2014).
Improved technologies and system designs can result in more efficient energy usage, and in turn, energy savings. Despite incremental improvements in efficiency over time, efficiency remains an untapped resource. According to a recent report by IEA Energy Efficiency, only 30% of global energy is currently subject to energy efficiency standards. Despite minimal energy efficiency policies in place, between 2010 and 2018 the average global improvement in primary energy intensity was 2.1% per year (IEA Energy Efficiency 2019).
Electrification and Alternative Fuels
Electrification of the energy system is the process of increasing the types of energy demands that are met through electricity, rather than burning fuels directly. Currently, most energy users are accustomed to drawing upon a variety of sources to meet their energy requirements. For example, at the household level, a family may use natural gas for heating and cooking, gasoline for their car, electricity for air conditioning, lighting and electronics. However, technology improvements provide new opportunities to accomplish more of these energy services using electricity. Doing so can yield substantial improvements in efficiency or performance while also increasing the benefits of power sector decarbonization (discussed in the next section).
Mark Jacobson’s studies on the U.S. energy system have found that converting from a combustion based system to one electrified by renewable sources would yield a ~39% reduction in end-use load with ~82% of this saving due to electrification and the remaining due to improving end-use efficiencies (Jacobson 2009, 2015).
Sources of Energy
Revolutionizing our energy system to stay below 2°C warming by 2100 will also require rapid deployment of renewable and low-carbon energy sources at sufficient scale to power our energy needs. Accelerating the timeline for the needed transition will take a focused effort and considerable political will. Currently, renewable energy sources supply only 14% of global primary energy, or 26% of global electricity generation. However, renewable energy capacity growth has been growing steadily in recent years (IEA, 2019) – exponential rates of change such as in the solar and wind markets, if sustained, have short doubling times. National or state goals are altering the rate of renewable energy sources being deployed. In some cases more aggressive goals are being set than those required by the participating parties of the Paris Accord. For example, California is working toward ambitious short- and long-term goals for carbon emission reduction more in step with the reductions required to stabilize the climate.
Global energy consumption increased by 2.9% in 2018. Growth was the strongest since 2010 and almost double the 10-year average. The demand for all fuels increased but growth was particularly strong in the case of gas (1,954 TWh equivalen, accounting for 43% of the global increase) and renewables (826 TWh, 18% of the global increase). In the OECD, energy demand increased by 954 TWh on the back of strong gas demand growth (814 TWh). In the non-OECD, energy demand growth (3,582 TWh) was more evenly distributed with gas (1,140 TWh), coal (989 TWh) and oil (547 TWh) accounting for most of the growth (BP Statistical Review of World Energy 2019). Graphic source: Our World in Data 2020.
Negative Emissions Technologies
Negative emissions, also known as carbon dioxide removal, refers to processes by which carbon emissions are sequestered in an effort to a) prevent additional accumulation of greenhouse gases in the atmosphere, and/or b) remove greenhouse gases that have accumulated in the atmosphere. If carbon emissions are sequestered at higher rates than they are emitted, the overall greenhouse gas concentration in the atmosphere could be reduced. Many scenarios that consider how to reduce emissions at the speed and scale required to meet warming targets below 2ºC expect that negative emission strategies will play some role. However, many of these strategies should come secondary to avoiding emissions to begin with, as they have significant economic and justice implications. Negative emissions can be achieved biologically by increasing natural carbon sinks or through chemical engineering processes. Negative emissions approaches can be classified into the following main categories (EASAC, 2018):
- Afforestation and reforestation
- Land and soil management
- Carbon Capture and Storage (CCS)
- Bio Energy with Carbon Capture and Storage (BECCS)
- Direct Air Capture (DAC)
Justice in the Transition
Of all the potential co-benefits of a low carbon energy system, one that is not necessarily assured is energy justice. If this important component is overlooked, our future energy system has the potential to exacerbate existing inequities or create new ones. But if done with intention, this can be a rare and vital opportunity to amend structures that have long inflicted damage and injustice on vulnerable communities and ecosystems around the world. In doing so, we can create a far more robust and equitable energy system, while bypassing opposition and friction to a clean energy transition.