Restoring tree cover is now firmly established as a strategy for removing carbon from the atmosphere to help tackle climate change.
But there is an elephant in the room when it comes to estimating just how promising a climate solution it is in different locations. This is “albedo” – the fraction of the solar radiation that is reflected from the Earth’s surface.
In essence, brighter surfaces – such as a large snowy expanse or a grassland – will generally reflect a high proportion of sunlight back into space. Trees, meanwhile, tend to be darker coloured and absorb more sunlight, keeping it on Earth – usually in the form of excess heat.
Because restoring tree cover often involves replacing brighter land covers – such as grasslands – with darker ones – namely, trees – this can lead to some degree of global warming.
In some locations, this warming can partially or even completely outweigh the benefit of increased carbon uptake by the trees. Many know of this problem, but it has been difficult to quantify the impact of albedo in specific locations.
In our new study, published in Nature Communications, we map albedo change from restoring tree cover and show that carbon-only estimates of the global climate benefits of tree-planting may be 20-81% too high.
Our maps reveal that the climate benefits of tree-planting in savannahs in Africa and central Asia would be the most reduced by albedo. But we show that it is possible to find places that provide net-positive climate mitigation benefits in all biomes.
Tree cover affects albedo
It is getting harder to ignore albedo when planning projects to restore tree cover for climate mitigation.
For example, a recent study published in Science showed that albedo, among other factors, could substantially reduce the climate mitigation benefit of restoring tree cover.
However, despite its importance, albedo is often only given a brief mention as an important factor in research attempting to quantify the climate benefits of restoring tree cover. Its impact is frequently not accounted for – or only via coarse adjustments.
In some places, restoring tree cover modifies albedo enough to dwarf smaller changes in carbon, leading to an overall (net) increase in global warming. In other locations, the impact of albedo does not outweigh the carbon removal, contributing to an overall global cooling effect.
Understanding and quantifying these variations in albedo and carbon change is crucial to the success of a project that aims to restore tree cover for climate mitigation.
Yet there has been a lack of tools to provide this information. Our study sets out to change that.
Mapping albedo change
Our study provides the maps that quantify the absolute and relative changes in albedo anywhere on Earth where we might grow trees.
We first created a series of 24 maps that quantified how albedo would change if an area transitioned from one of four open land cover classes – such as grassland or croplands – to one of six different forest-cover classes, such as deciduous broadleaf or evergreen needleleaf forest. These are useful for individual projects that know their starting and end conditions.
However, to examine general global patterns, we used a data-driven approach to model the albedo change resulting from the “most likely” open-to-forest transition for each part of the world. We then combined that with a map of maximum potential carbon storage to map net climate impact in carbon dioxide equivalents.
In this map (below), red and orange shading indicates regions where restoring tree cover leads to net warming and blue indicates regions where restoring tree cover leads to net cooling.
The map shows that, in many places, increasing tree cover is likely to contribute to global warming. These include the dryland ecosystems of central Asia and the Sahel region of Africa, as well as northern reaches of North America, Europe and Asia.
However, all biomes had at least some climate-positive locations, indicating that the coarse exclusions used in the past have missed opportunities. Moreover, some locations experience little to no albedo change, such as in south-east Asia, central Africa and the Amazon.
This map makes it possible for people to determine the best places to restore tree cover to achieve climate mitigation, as well as evaluate different scenarios of where restoration of tree cover might happen.
For example, we examined three previously published global studies of large-scale increases in tree cover. We find that, after accounting for albedo, the global climate mitigation benefit of restoring tree cover may actually be 20-81% lower than expected from carbon-only estimates.
Notably, the study with the greatest deduction included large areas of tree-planting within the tundra and other locations where we predict very negative climate outcomes. We show that constraining this study’s tree-planting to only the more climate-positive areas – about a third of the total area (311m hectares instead of 889m hectares) – would lead to a 2.5-fold increase in mitigation potential.
This demonstrates the value of strategic project placement to maximise climate benefit, because it is possible to achieve more mitigation with less investment of space.
Forest restoration projects
Encouragingly, our study also finds that hundreds of thousands of on-the-ground tree-planting projects tend to be concentrated in places where the potential for carbon removal is high and albedo change is moderate.
One example is the moist tropical ecosystems in Brazil and Indonesia. Most of these on-the-ground projects can be found at Restor, a data-driven and community-based platform that aims to accelerate restoration and makes it possible for the first time to evaluate outcomes of the global restoration movement.
This suggests that ongoing or planned projects are concentrated in places that are good for achieving climate mitigation. However, the majority – around two-thirds – of these on-the-ground projects still face an albedo offset of at least 20%, indicating that most – if not all – projects should consider albedo change in their accounting.
None of this is to criticise projects that fall in places with negative climate outcomes. There are many wider reasons for restoring tree cover in a given landscape, beyond climate mitigation, including cleaner water, wildlife habitat, stabilised soils, sustainable livelihoods and cooler local temperatures.
However, for projects where the emphasis is on achieving climate mitigation, it is important to consider changes in albedo alongside changes in carbon removal, especially now that the tools are available to do so.
In general, climate accounting is not for the faint of heart. There are many factors such as albedo that can alter the total climate mitigation of natural climate solutions. However, we are in a critical time when pragmatic decisions need to be made now about which climate solutions to deploy and where.
Alongside our study, we have produced a dedicated web platform – called “naturebase” – to help policymakers, practitioners, communities and governments identify where, why and how to implement nature-based projects with the highest carbon mitigation.
This tool includes maps, data and case studies to show how different natural climate solutions – including restoration of tree cover – could benefit the climate across the world.
Policymakers and land managers are under growing pressure to make complex choices in line with global agreements. We hope that the science in our study and the tools in the naturebase platform will help enable smarter, more nature-positive decisions.
The post Guest post: Mapping where tree-planting has the greatest climate benefit appeared first on Carbon Brief.
Guest post: Mapping where tree-planting has the greatest climate benefit
Claver Gatete is Executive Secretary of the UN Economic Commission for Africa. Jason Veysey is Energy Modeling Program Director and Senior Scientist at the Stockholm Environment Institute. Lisa Sachs is Director of the Columbia Center on Sustainable Investment at Columbia University.
The case for global energy transition has rarely been clearer. The closure of the Strait of Hormuz earlier this year exposed the cost of unplanned, fossil-dependent systems, while the falling cost of renewables, the rising penetration of electric vehicles, and the growing value of demand flexibility have made the direction of travel obvious. The benefits of a clean, secure, integrated system are no longer in dispute. What remains unclear is how to build it.
Countries around the world have called for faster renewable energy deployment and alternative energy arrangements. A secure, affordable, resilient, decarbonised system requires specific investments in specific places in a specific sequence, optimised across sectors and borders. But very few governments have the analytical foundation to translate those imperatives into investment.
The two instruments that are supposed to determine investment priorities for decarbonisation – Nationally Determined Contributions (NDCs) and country platforms – cannot answer the most basic question facing any country undertaking an energy transition: what should the energy system look like?
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To close this gap, every country needs a bankable, economy-wide optimisation model for its energy system. A model is not a plan, but it can help answer the critical question of what the future energy system should look like. It shows how optimal scenarios vary as assumptions and policies are adjusted, calculates investment requirements and sequencing, and quantifies how system costs are affected by assumptions, policies, and exogenous variables like trade policy and financing terms.
Tool for efficient investment
Optimisation is a simplified way of simulating an energy system, but it can be an extremely powerful tool for moving energy planning from reactive (how do we manage the disparate actions in the energy system?) to intentional (what energy system underpins our national objectives?). A model can show how optimal scenarios vary as assumptions and policies are adjusted, and how investment requirements are quantified and sequenced.
Optimisation models can treat the energy system and the sectors it serves as an integrated whole, optimising across sectors and projects in ways that can be mutually reinforcing. If considered independently, growth in industrial demand, transport electrification, and digital infrastructure can add stress to the energy system. But an optimised plan can arrange these and other changes in an efficient, synergistic way.
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New load can be added where low-cost power is available; industrial customers can ensure the viability of investments in energy supply; electric vehicle charging policy can smooth load curves and reduce costs for all consumers.
Additionally, optimisation modeling can also change the financeability of investments. Taken alone, each project faces uncertainty about the rest of the system, which raises the cost of capital and causes projects to stall or unwind after contracts are signed. A coherent, optimised plan makes visible the coordination that private capital would otherwise have to bet on: identified offtake, sequenced and committed transmission, contracted power supply, and so on.
What COP31 and COP32 should do
The upcoming COPs in Turkey and Ethiopia can shift the center of gravity of international climate cooperation from fragmented commitments to planning. Three moves are urgently needed.
First, optimised, economy-wide, long-term energy system planning must be the foundation on which any meaningful NDC, country platform, or finance commitment rests. NDCs are typically drafted by environment or single-line ministries, with limited cross-sectoral input from ministries of energy, finance, and planning. They contain targets, derived from sectoral strategies or national commitments, not from an analytically grounded picture of what the energy system should look like and what investments would make it work. Country platforms are generally a portfolio of investments assembled from existing project pipelines, rather than derived from a system-level analysis of what an optimised, decarbonised energy system would require.
Second, recognise regions as a key planning unit. Modern integrated energy systems are inherently regional. Renewable endowments are unevenly distributed; balancing variable supply across borders lowers aggregate cost, reduces redundant backup capacity, and unlocks economies of scale no individual nation can achieve. Many energy investments in Southeast Asia, East Africa, Southern Africa and Central Asia may only be financeable in a regional context. Assessing domestic infrastructure without regional optimisation perpetuates the perception that decarbonisation is more expensive than it is.
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Third, finance the planning capacity. A coordinated commitment by multilateral development banks, bilateral donors, and philanthropic partners to help every region and its constituent countries develop and maintain their own modelling capability, with open-source tools and regional analytical hubs, would close the most consequential gap in the current architecture. The cost is small relative to current spending on country platforms, failed project preparation, and misallocated infrastructure investment.
This includes supporting regional institutions such as the ASEAN Centre for Energy, the African Energy Commission, regional power pools, and the Latin American and Caribbean Energy Organization to determine what optimised regional systems require. Country-by-country pledging, repeated at every COP, will not deliver what meaningfully integrated systems can.
The 2026 energy crisis made the cost of unplanned, fossil-dependent systems newly visible. That window of clarity will close. The international community should seize the moment to build the planning foundation that has been missing for thirty years, rather than commissioning another round of NDCs or pledges, striving for outcomes neither was designed to deliver.
The post Every country needs a model to help optimise its energy transition appeared first on Climate Home News.
Every country needs a model to help optimise its energy transition
The world is currently experiencing what is expected to become the strongest El Niño on record – dubbed a “super El Niño” by many.
El Niño is the warm phase of a recurring climate pattern in the tropical Pacific that releases heat from the ocean into the atmosphere.
This temporarily raises global temperatures and reshapes rainfall and extreme weather around the world – impacting the lives of billions of people.
The current El Niño event began in June and is expected to last into 2027.
El Niño is part of a wider climate pattern called the El Niño-Southern Oscillation (ENSO) cycle.
The ENSO cycle also has a cool phase, known as La Niña, as well as a “neutral” phase. El Niño and La Niña events typically last between nine and 12 months, but can go on longer.
Below, Carbon Brief explains how the ENSO cycle works, its impacts on extreme weather and global temperatures and why this El Niño event is projected to be the most intense since records began.
The post Explainer: How the ‘super El Niño’ will reshape the world’s weather appeared first on Carbon Brief.
https://interactive.carbonbrief.org/el-nino-explainer/index.html
The second-largest reservoir in the US reached a record-low water height on Saturday – just days after the country’s largest reservoir broke its own record.
Both Lake Mead and Lake Powell are located on the Colorado River.
They provide water for populations across seven US states in the south-western US, with around 40 million people getting some or all of their municipal water from the Colorado River.
The river also provides water for around 5.5m acres (22,258 square kilometres) of farmland across Colorado, Arizona, California and the other states in the river basin.
Experts tell Carbon Brief that climate change, population growth and over-consumption are all contributing to the current record-low levels of the reservoirs.
Record lows
At full capacity, Lakes Mead and Powell can hold a combined 68 cubic kilometres of water – enough to supply all household consumption in the contiguous US for nearly 1.5 years. However, the water level in both reservoirs has been declining for decades.
The chart below shows the water level of Lake Mead, in metres above mean sea level. The reservoir, which began to fill in 1935 following the construction of the Hoover Dam, has a “full pool” maximum capacity of 347.60 metres. The water level in Lake Mead reached a record low of 317.11 metres on 7 August.
The following chart shows the water level of Lake Powell, in metres above mean sea level. Lake Powell’s full-pool level is 1,127.76 metres.
While the reservoir reached its maximum capacity several times in the 1980s, it has not done so since. On 15 August, the water level in Lake Powell was recorded at a new record-low of 1,072.87 metres.
Both reservoirs have continued to decline in the days since breaking their respective records. The downward trend will largely continue in both lakes until next spring, when the snowpack in the mountains of the Upper Colorado River Basin begins to melt, says Dr Jack Schmidt, a senior research scientist at Utah State University’s Center for Colorado River Studies. He tells Carbon Brief:
“The big dilemma of the moment is that we’re only in the middle of August, and we have no assurance of what the coming winter will be. The only thing we can be sure of is that we will be depleting overall total basin reservoir storage from now until, roughly, early April.”
Compounding factors
The record lows across the two reservoirs are the result of several compounding factors, experts tell Carbon Brief.
Since the turn of the 20th century, the amount of water flowing along the Upper Colorado River has declined by about 20%. Research suggests that half of this decline can be attributed to human-induced climate change.
Most of the river’s streamflow comes from the snowpack of the Upper Colorado River Basin, which stretches across five western US states but is primarily located in Colorado and Utah.
This region has been gripped by a historic “megadrought” for more than a quarter of a century. Nearly half of the megadrought’s intensity over 2000-18 is attributable to climate change, according to a 2020 study.
At the same time, the increasing population in the US south-west has put added pressure on the Colorado River’s water supply. The number of people obtaining some or all of their water from the Colorado system has grown by 15 million (around 60%) since 1992.
Schmidt tells Carbon Brief:
“There’s an ultimate cause of the present water crisis, and there’s a proximate cause. The ultimate cause is a warming climate, a warming planet and a pretty clear correlation between warming conditions and decreased runoff in the Colorado River Basin.
“The proximate cause is that in this messy democratic republic of ours, big policy decisions that match the variability of the climate occur painfully slowly – with intense political negotiations – and only incrementally.”
On 31 July, the US Bureau of Reclamation, which manages water resources in the western US, released an environmental impact statement on its proposed post-2026 strategy for managing Lakes Powell and Mead. The strategy itself has not been released yet.
Schmidt notes that the statement does appear to give the Bureau flexibility to “respond to crisis” by reducing the delivery of water to several states. However, he adds:
“They acknowledge it won’t work if we just stay critically dry, and of course every climate model for the 21st century, especially with a continually warming planet, says that that’s exactly what’s going to happen.”
The post Analysis: The two largest reservoirs in the US have hit record-low levels appeared first on Carbon Brief.
Analysis: The two largest reservoirs in the US have hit record-low levels
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