Table of Contents
Connecting Energy and Climate
Climate action is fundamentally about reducing the amount of greenhouse gases that humans add to the atmosphere and enhancing the ability of natural and human systems to cope with change. Because most human-made greenhouse gas emissions come from producing and using energy, any serious climate strategy must transform the energy system. Renewable energy lies at the center of this transformation.
In simple terms, using renewable energy means replacing energy sources that release large amounts of carbon dioxide and other greenhouse gases with sources that emit little or almost none during operation. This shift directly targets the root cause of climate change and is a cornerstone of global efforts to limit temperature rise.
How Renewable Energy Reduces Emissions
Most climate policies and scientific assessments treat renewable energy as one of the main tools for cutting emissions. The replacement of fossil fuel use by renewable sources changes the amount of greenhouse gases released per unit of useful energy.
A widely used way to express this idea is through emission factors. An emission factor tells us how much greenhouse gas, often expressed as carbon dioxide equivalent, is released for each unit of energy produced. For electricity, it is common to use kilograms of $\text{CO}_2\text{e}$ per kilowatt-hour.
A simple relationship for estimating emissions from electricity is:
$$\text{Emissions} = \text{Electricity generated} \times \text{Emission factor}$$
where emissions are in $\text{kg CO}_2\text{e}$, electricity in kWh, and the emission factor in $\text{kg CO}_2\text{e} / \text{kWh}$.
In practice, when coal or gas power is replaced with solar, wind, or other renewable generation, the average emission factor of the power system decreases. Over time, as more renewables are added and fossil generation is retired or used less, the total emissions from electricity fall.
The same logic applies in other sectors. When renewable electricity replaces fossil fuels for heating buildings, powering vehicles, or running industrial processes, total emissions decrease because the energy source has a lower emission factor.
Renewable Energy in Mitigation Strategies
Climate mitigation refers to actions that reduce the causes of climate change. Renewable energy is one of the primary mitigation tools, and it appears in national plans, corporate strategies, and international scenarios that explore how to limit warming.
Mitigation strategies often combine three linked elements. The first is using energy more efficiently so that less energy is needed to deliver the same services. The second is switching from high carbon fuels to lower carbon or zero carbon options, such as moving from coal to renewables. The third is changing technologies and infrastructures so that they can use low carbon energy effectively, for example through electrification of transport.
In this combination, renewables provide the low emissions supply that makes switching possible. As electricity grids become cleaner due to renewables, every electric device and vehicle connected to the grid also becomes cleaner over its lifetime, as long as average grid emissions continue to fall.
Many global scenarios that aim to keep temperature rise well below a certain threshold show a rapid expansion of renewable energy as a non negotiable component. They typically feature high shares of wind and solar in electricity, increased use of modern bioenergy and geothermal in heat and industry, and renewable-based fuels and hydrogen in sectors that are harder to electrify directly.
Decarbonizing Key Sectors With Renewables
Energy use is often grouped into three broad sectors, electricity, heat and buildings, and transport, along with uses in industry. Renewables play different but connected roles across these areas.
In electricity, renewables offer a clear path to deep decarbonization. Solar photovoltaics and wind power, complemented by hydropower, geothermal, and other sources where available, can provide a large share of total generation. As their share grows, overall emissions from the power sector can drop sharply, especially when fossil plants are phased down and their role shifts to backup or is replaced by storage and flexible demand.
In buildings and heating, renewable options include direct use of solar heat, modern biomass, and geothermal, as well as electric heating systems that run on renewable electricity. Heat pumps are an example of a technology that, when powered by a low carbon grid, can significantly cut the emissions associated with space heating and hot water.
In transport, renewable energy supports climate action both through direct electrification and through renewable-based fuels. Electric vehicles charged from a renewable rich grid can greatly reduce emissions compared to vehicles that burn fossil fuels. For parts of transport that are more difficult to electrify, such as some long distance shipping or aviation, renewable-based fuels and other synthetic options produced from renewable electricity can offer routes to lower emissions.
In industry, renewable electricity can supply power for machinery and processes, and in some cases heat. Where very high temperatures or specific chemical reactions are needed, renewable-derived fuels and hydrogen can act as lower carbon inputs. The potential for renewables in industry is closely linked to broader changes in technologies and materials that will be explored elsewhere in the course.
The Role of Renewables in Long-Term Climate Goals
Long-term global climate goals, such as achieving net zero emissions within a certain time frame, depend on a deep restructuring of energy systems. In these visions, renewable energy is not a minor supplement to fossil fuels, but becomes the main source of primary energy.
Scenarios that reach net zero typically share some common energy features. Electricity generation shifts from being a significant source of emissions to becoming almost entirely supplied by low carbon sources, with renewables forming the majority. Total electricity use grows, because electricity replaces fossil fuels in many applications. Renewables provide the bulk of this expanded electricity, supported by storage, more flexible demand, and improved grid management.
At the same time, direct use of renewables for heating, cooling, and low temperature processes becomes more common, and renewable-based fuels and hydrogen complement these changes in sectors where direct electrification is not practical or timely. The combined effect is a large decline in direct fossil fuel combustion.
It is important to recognize that in some net zero pathways, a certain amount of remaining emissions is offset by activities that remove carbon dioxide from the atmosphere. Although these removal methods are not the main subject of this chapter, they illustrate another reason why rapid renewable deployment is vital. The more emissions are cut with renewables and efficiency, the less pressure there is to rely heavily on removal technologies, which often carry uncertainties and constraints.
Co-benefits and Systemic Effects of Renewable Deployment
The contribution of renewables to climate action is not limited to direct emission reductions. Widespread renewable use can also change energy systems and societies in ways that support broader climate goals.
When countries adopt renewables, they often reduce their dependence on imported fossil fuels. This can increase energy security, make economies less vulnerable to fuel price swings, and encourage more stable long-term planning. As renewable technologies are built and maintained, they can stimulate new industries and jobs that are compatible with climate objectives, helping to align economic development with emissions reduction.
There are also important interactions between renewables and air quality. Replacing fossil fuels with cleaner energy sources tends to reduce harmful air pollutants that affect human health. Although this is not the same as reducing greenhouse gases, the same actions often achieve both at once, reinforcing the case for rapid renewable deployment within climate policy.
On the technical side, integrating large shares of renewables into existing grids and infrastructures requires improvements in flexibility, storage, and system management. These changes make energy systems more adaptable and better able to cope with climate related shocks. For example, a diversified and distributed renewable system can be less vulnerable to certain climate impacts than a system highly concentrated in a small number of large fossil or nuclear plants.
Limits and Complementary Measures
While renewables are essential for climate action, they are not a complete solution on their own. Their effectiveness in reducing emissions depends on how they are introduced and what they replace.
If new renewable capacity simply adds to total energy supply without displacing fossil use, the climate benefits are smaller. The greatest impact occurs when renewables are combined with policies and market designs that actively reduce fossil generation and consumption over time. In many regions, specific measures are needed to retire or repurpose existing high emitting plants rather than keeping them fully active alongside renewables.
Moreover, climate action includes not only mitigation but also adaptation and resilience. Renewables mainly address the cause of climate change by cutting emissions. Other actions are still required to prepare for climate impacts that are already unavoidable. Some renewable energy systems can themselves be designed to be more resilient to changing weather patterns and extremes, but this is an additional design challenge rather than an automatic outcome.
Finally, emission reductions from renewables are closely connected to broader patterns of consumption, land use, and material use that will be discussed elsewhere in the course. Efficient, thoughtful use of energy and resources amplifies the benefits of renewable technologies and reduces the strain on ecosystems and societies.
Positioning Renewables Within Climate Action
Viewed within the broader landscape of climate responses, renewable energy sits at the core of transformative change in the energy system. It allows societies to maintain and evolve essential services such as lighting, mobility, heating, cooling, and industrial production, while steadily cutting the emissions that drive climate change.
In practice, this means that many climate strategies start by asking how quickly and fairly renewable energy can replace fossil fuels in electricity, heat, transport, and industry, and how the supporting systems of finance, policy, infrastructure, and behavior can be aligned with this shift. The rest of the course will explore these supporting elements, but the central idea remains clear. Any credible path to stabilizing the climate relies on a large scale, sustained, and well managed expansion of renewable energy.