A Pragmatic “Glide Path” for Coal Phase Out

Most countries are moving toward renewable energy and have defined – often timestamped – plans to phase down or phase out coal. These commitments reflect growing recognition of the health, environmental, and climate impacts associated with coal-fired power generation. However, coal power will not disappear overnight. In several large and fast-growing economies, many coal plants are relatively new and are expected to operate for decades. For example, more than two-thirds of the coal fleet in India is under 20 years old, with around a third under a decade old.

These plants were financed, built, and integrated into power systems with the expectation of long operating lives. In economically challenged regions such as emerging Asia, where the majority of the global coal fleet operates, early closure of coal plants – well before their expected 40-60-year lifetimes – is costly and often unattainable without substantial external finance. Utilities and governments face complex trade-offs between environmental objectives, energy security, affordability, and financial stability. As a result, coal plants that are already built are likely to continue operating for some time, even as countries expand renewable energy capacity.

This creates a fundamental challenge for the energy transition. Coal power remains a major source of air pollution and climate-warming emissions that harm human health and the environment. Even as coal capacity declines, there is a real risk that pollution persists – or even worsens – if the remaining fleet is not managed effectively. Simply assuming that emissions will fall automatically as coal use declines overlooks the operational realities of power systems in transition. What is needed is a practical, step-by-step approach that reduces emissions from coal in the near term while supporting a credible pathway toward eventual phase-out.

The idea of a “Glide Path”

A “Glide Path for Coal” is a planned, gradual strategy that reduces pollution year by year as coal plants move toward retirement. Rather than focusing solely on end-points such as full phase-out dates, a Glide Path emphasises how coal plants are operated, prioritised, and retired over time. This approach recognises that coal generation may persist during the transition but seeks to minimise its environmental and health impacts as rapidly and efficiently as possible.

A recent Global Environment Facility (GEF) project led by Macquarie University evaluated emissions from the global coal fleet under different future energy and policy scenarios, including business-as-usual operation, early retirement, and the installation of air-pollution control devices. The analysis considered current and planned energy policies, as well as potential future strategies, with a particular focus on emerging economies where coal remains central to power supply.

The findings were clear and consistent across regions. Early closure of coal plants delivers far greater emission reductions than technical fixes alone. Avoiding the construction of new coal plants has an especially large impact, particularly in countries that already have excess coal capacity. Installing pollution-control equipment does reduce emissions, but these measures cannot match the benefits of retiring the dirtiest and least efficient plants sooner. In other words, which plants operate, and for how long, matters at least as much as how individual plants are retrofitted.

These conclusions may seem intuitive, yet they are not always reflected in policy or investment decisions. In many cases, pollution controls are promoted as a way to extend plant lifetimes, rather than as part of a managed decline.

A Glide Path would reframe this logic, using emissions performance to inform decisions about dispatch, refurbishment, limited operation, or early retirement.

Operational challenges in a transitioning power system

As coal fleets shrink, an important and often overlooked challenge emerges. The remaining coal plants are increasingly required to operate more flexibly to support growing shares of variable and non-dispatchable renewable energy such as wind and solar. Instead of running steadily in baseload mode, coal plants are often used as backup capacity, filling gaps when renewable output is low or demand is high. This shift in operating patterns has significant implications for emissions.

Units may be ramped up and down frequently, operated at very low load for extended periods, or restarted after long shutdowns. In some cases, plants that were expected to retire may be brought back into service during periods of system stress. These modes of operation differ substantially from the steady conditions under which coal plants were designed and optimised.

Frequent cycling reduces thermal efficiency, increases fuel consumption per unit of electricity generated, and can lead to higher emissions of both greenhouse gases and local air pollutants. Pollution-control equipment may not perform optimally under these conditions, and in some cases may be switched off or bypassed to avoid equipment damage during rapid load changes. The result is that emissions intensity can increase even as total coal generation declines.

Because official emissions inventories and projections typically assume smooth, stable operation, actual emissions from coal plants in systems undergoing rapid renewable expansion are likely higher than reported. Studies suggest emissions can increase by 25% or more during flexible operation. The assumption that coal emissions decline smoothly as fleets move toward closure is therefore optimistic at best, and potentially misleading. A planned Glide Path helps to identify and manage these risks by aligning operational decisions with emissio-nreduction objectives.

Learning from fleet-level approaches

The value of a fleet-level perspective is illustrated by a project undertaken for the Government of Indonesia by the International Centre for Sustainable Carbon on behalf of the US Department of State. Conducted under the auspices of the UN Minamata Convention, the project focused on mercury emissions, but the methodology and insights were applicable to all major pollutants.

Rather than assuming uniform performance across the coal fleet, the project assessed the entire Indonesian fleet – 111 units – on a unit-by-unit basis, ranking plants according to emissions over their remaining planned operating lifetimes. This approach revealed significant variation in performance between units, driven by differences in age, technology, fuel quality, maintenance practices, and operating conditions.

By identifying cleaner and dirtier plants, the analysis enabled a more strategic approach to fleet management. It became possible to determine which units should retire first, which should operate only during critical periods, and which might remain temporarily for energy security but under tighter pollution controls. This type of analysis supports more nuanced decision-making than blanket policies applied uniformly across all plants.

Importantly, this approach does not require immediate closure of all coal capacity. Instead, it prioritises actions that deliver the largest emissions reductions in the shortest time, while maintaining system reliability. It also provides a transparent framework for engaging utilities, regulators, and investors in discussions about transition pathways.

Integrating health, equity, and social considerations

The primary objective of a Glide Path would be to reduce harmful emissions as quickly as possible without risking power shortages or economic disruption.

However, emissions data alone do not capture the full impact of coal generation. The location of plants relative to population centres, prevailing weather patterns, and underlying social vulnerability all influence the extent of health impacts.

A truly effective Glide Path therefore needs to integrate emissions performance with assessments of population exposure, public health outcomes, and social equity.

Communities located near coal plants often face disproportionate health burdens, including respiratory and cardiovascular disease, and these impacts frequently overlap with broader patterns of socioeconomic disadvantage.

Models such as those being developed by EPRI in the United States demonstrate how power-system infrastructure can be overlaid with socioeconomic and demographic data to assess health risks under different policy and decarbonisation scenarios.

These tools allow analysts to compare reference systems with alternative pathways, identifying where changes in generation patterns could reduce exposure and improve health outcomes. As analytical capabilities improve, it is increasingly possible to prioritise electricity production from sources and locations that minimise human exposure, taking meteorological conditions into account.

This represents a significant evolution in power-system planning, shifting the focus from purely technical or economic optimisation toward outcomes that explicitly incorporate public health and social wellbeing.

Managing the coal fleet as a system

A Glide Path approach would shift attention away from individual plant retrofits toward the strategic management of the entire national coal fleet. Key elements of approach include:

• Unit-by-unit performance analysis, ranking plants by efficiency, emissions, age, and operating costs to inform decisions on early retirement, refurbishment, or limited operation.

• Operational optimisation, using models and tools to minimise efficiency losses and emission increases during flexible operation, including improved maintenance practices and revised operating protocols.

• Dispatch guidance, enabling utilities and system operators to prioritise the cleanest and most efficient units on a real-time basis, rather than relying solely on traditional merit-order dispatch.

• Forward planning, aligning short-term operational decisions with longer-term phase-down and phase-out objectives to avoid lock-in or unintended consequences.

This system-level perspective allows countries to achieve emissions reductions more quickly and at lower cost than approaches focused exclusively on individual assets.

It also provides a clearer narrative for investors and development partners, linking near-term actions with long-term transition goals.

The importance of a just transition

Coal plant closures have significant social and economic implications. Workers, families, and entire communities can be affected by the loss of employment and associated economic activity. Any serious transition strategy must therefore include robust measures to support a just transition.

This includes retraining and reskilling programmes for displaced workers, support for economic diversification in coal-dependent regions, and inclusive planning processes that involve local communities in decision-making. Opportunities to repurpose coal sites for energy storage, hybrid systems, or other forms of infrastructure can also help mitigate economic impacts and maintain local employment.

A Glide Path does not eliminate these challenges, but it allows them to be anticipated and managed more effectively. By providing a clearer timeline and prioritisation framework, it creates space for proactive planning rather than reactive crisis management.

Key takeaways

Coal will remain part of the energy mix in some countries for decades, even as renewable energy expands rapidly. Early retirement of the most polluting plants is the most effective way to reduce emissions, but pollution from remaining plants may be higher than official estimates suggest due to changing operating patterns. Managing coal as a coordinated fleet—rather than as a collection of individual assets—enables faster and smarter emissions reductions while maintaining energy security. Integrating health, equity, and social considerations is essential for long-term success. A well-planned Glide Path would allow countries to protect public health, cut emissions rapidly, and prepare systematically for a future without coal.

A large Glide Path project was proposed as part of the GEF study cited in this article and is currently awaiting funding with the aim of developing fleet strategies for 5 selected coal-reliant emerging economies.

Note: The GEF report discussed in this article is available as a free download from the UNEP website and is accompanied by an interactive dashboard that allows users to view emissions globally and regionally under different future energy and policy scenarios.

Lesley Sloss