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The pros and cons of planting trees to address global warming

Posted on 23 March 2020 by Guest Author

This is a re-post from Yale Climate Connections by Bruce Lieberman

It seems like such a simple, straightforward, empowering idea: plant trees – a lot of trees – all over the world, and watch the planet’s temperature fall.

Who doesn’t love a tree or two, even far more – the right tree in the right place?

Along with the refreshing shade they provide on hot days, trees of course also store carbon, and they’ll suck it right out of our fragile atmosphere as they grow. Who could argue with more trees, more forests – more shade! – in a warming world? Nary a soul, one suspects, whether of conventional “tree hugger” category or rabid climate science detractor.

Earlier this year, the one-trillion tree campaign was big news at the World Economic Forum in Davos, Switzerland. Salesforce founder Businessman Marc Benioff announced at the meeting that his company will “support and mobilize the conservation and restoration of 100 million trees over the next decade.”

Back in Washington, D.C., President Trump and Republican lawmakers said they too support the international campaign – although Arkansas Republican Rep. Bruce Westerman came under fire for proposing a “Trillion Trees Act” that would pair a commitment to planting trees with a plan to increase logging on public lands. Numerous other Republican representatives are endorsing the trees effort.

Cautions against just randomly digging and planting

Over the past few weeks, chatter has picked up that planting trees is only one piece of the puzzle when it comes to combating climate change. Trees are a good thing, but:

  • We also need to protect existing forests – the Amazon, for example.
  • We need to ramp up wind, solar, and geothermal energy.
  • We need to burn less fossil fuel.
  • We need to eat more of the right foods and less of the wrong ones and, above all else, eat sustainably.
  • We need higher vehicle-mileage standards and more electric cars.
  • We need to get our act together so we can better adapt to rising seas, more droughts and wildfires, and unpredictable swings in weather.

Like other initiatives to tackle climate change, planting trees requires some forethought. Recent news coverage of the trillion tree campaign points to several things people should be thinking about before digging and planting.

Authors of a 2019 study from the Swiss research university, ETH Zurich, estimated that the planet can support about 2.5 billion more acres of newly planted trees – without tearing down cities and doing away with farms. And they say those trees could store about 200 gigatons of carbon (GtC) once they mature. That’s equal to one-third of all the carbon that humans have emitted into the atmosphere as carbon dioxide pollution, the authors claimed. The New York Times summarized the study last year.

Researcher: ‘Nations absolutely should plant and protect as many [trees] as possible. … But it’s also a limited and unreliable way of addressing climate change.’

Scientist Zeke Hausfather, long a regular contributor to Yale Climate Connections, suggested in a series of tweets at the time that the study was misleading on a few counts. For one thing, cumulative emissions from land use and burning fossil fuels were closer to 640 GtC, “so removing 200 GtC would represent one-third of historic emissions.” Hausfather also pointed to the practical and economic challenges of planting trees on every acre of available land.

India is intimately familiar with this challenge. Last summer the country planted hundreds of millions of trees as part of an initiative to keep one-third of its land area covered in trees. But the nation’s high population and rapid industrialization pose challenges to sustained reforestation. Only about 60% of the saplings are expected to survive – the rest succumbing to disease and a lack of water.

A Skeptical Science article by Dana Nuccitelli, a regular contributor to Yale Climate Connections and an environmental scientist, cites additional studies that have raised several other key points. Among them:

  • Tundra and boreal regions unpopulated by trees play an important global role in reflecting energy from the sun back into space. Planting trees in these regions would darken landscapes at these high latitudes, causing them to absorb energy from the sun rather than reflect it – ultimately contributing to higher global temperatures and offsetting cooling created by planting trees.
  • The ETH Zurich researchers mistakenly considered natural savannas, grasslands, and shrublands as places where forests could be restored.
  • And in their ETH Zurich study, they estimated a carbon sequestration rate of 0.22 GtC per million hectares (i.e., for every 2.47 million acres). But 0.22 GtC is twice the amount cited by previously published estimates.

Trees deserve a ‘moment’ of fame, but keep reality in mind

So while the right kinds and numbers of tree species in the right places have lots of appeal, big questions remain over exactly what can be accomplished by planting one trillion trees – and whether it may cause more harm than good.

James Temple, senior editor for energy at MIT Technology Review, summed up the view of many experts in a January 28 piece when he wrote:

“It’s great that trees are having a moment. Nations absolutely should plant and protect as many as possible. … But it’s also a limited and unreliable way of addressing climate change.”

Temple raised a few more important points, some of which have been echoed elsewhere. Among them: trees take time to grow and reach maturity – decades and even centuries for redwoods and other behemoths that can store massive amounts of carbon. If you think you’re going to immediately offset your carbon footprint from flying across the country by planting a tree … think again.

Another point Temple made: You really have to work the numbers to get a true sense of the challenge. For example, he wrote, the U.S. produced 5.8 billion gigatons of carbon dioxide emissions in 2019. To offset that much CO2 pollution, you’d have to plant a forest – and wait for it to fully mature – that is more than twice the size of Texas.

The one-trillion tree campaign raises still more questions for forest ecologists – one of them having to do with biodiversity. If the campaign results in what are essentially tree plantations lacking biodiversity and genetic variation, often referred to as monoculture, those artificial forests won’t get very far.

“People are getting caught up in the wrong solution,” Forrest Fleischman of the University of Minnesota told The Verge in late January. “Instead of that guy from Salesforce saying, ‘I’m going to put money into planting a trillion trees,’ I’d like him to go and say, ‘I’m going to put my money into helping indigenous people in the Amazon defend their lands.’ That’s going to have a bigger impact.”

A campaign to plant “one trillion trees” sounds ambitious, it sounds daring, and it sounds exciting. And in many ways it could be all of those. But keep in mind that since 2015 and just in the Sierra Nevada – that sliver of mountain habitat that runs along the spine of California – nearly 150 million trees have died, victims of drought, disease, and invasion by beetles. Warmer winters have contributed to a population explosion of these destructive insects, and it’s a story being played out across the American West where forest fires are growing in frequency and intensity.

So maybe we can plant a trillion trees around the globe. But if we don’t do much else about climate change, will we just be fueling the fire?

So maybe we can and should plant a trillion trees around the globe. Go for it. But a wide array of experts insist that if we don’t also take numerous other actions to address climate change – specifically including major cuts in fossil fuel emissions and in particular carbon dioxide – we may just be fueling the fire.

In the end, it comes down to more trees and lots of other actions, not to more trees or.

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Comments 1 to 14:

  1. "It seems like such a simple, straightforward, empowering idea: plant trees – a lot of trees – all over the world, and watch the planet’s temperature fall." I seriously doubt anybody has said that- so what's the point of being negative? Planting lots of trees- in the right areas- with the right mix of species is a good thing. Supporting this idea would be more productive than having a negative attitude about it and again, nobody is saying it's going to cool the climate. As a forester for 47 years and still working- I say planting trees and better managing forests is a win-win for everyone. By the way, that Yale site doesn't allow comments- though its sister web site "Yale 360" does.

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  2. As I have stated many times here at Skeptical Science, this is the wrong biome.

    Trees do have their ecosystem functions and obviously protecting and restoring forests is a good thing, but it is not the biome responcible for cooling the planet. Thus this is more like using AGW as an excuse to plant trees rather than an actual solution designed to reverse AGW.

    I am glad Dana Nuccitelli wrote about the flaws in using the wrong biome to reverse AGW, but I am surprised how resistant people are, even here.

    Allan Savory has come on this very site and tried to explain it. Probably by far the best expert scientist on the planet regarding grasslands restoration and how this in fact is the correct biome to accomplish the task.

    I myself have posted significant numbers of published science when and where I can find it. And I have been doing this for years here.

    We can even trace the original tree planting idea back to a "merchant of doubt" denial and obfuscation proposed by Freeman Dyson. He did have some minimal expertise, but not really in the climate science field long enough to be considered a reliable source.

    Yet this "tree planting" myth still persists over actual working scientists that have dedicated their entire lives to this one specialty? I am always confounded by this. Is it really so hard to understand that carbon on the surface is more likely to decay back into the atmosphere than stay sequestered long term as the carbon deep below the surface? Is it so hard to understand that C4 grasslands have much higher albedo, lower humidity from transpiration, and much higher efficiency of photosynthesis, while putting all these "ecosystem services" under the surface where they are protected?

    I have no problems with planting trees when and where we can, but really this is not helping much. 

    And please. Lets be honest here. The real reason the grasslands solution is being ignored or discounted is due to all the prime bits of land being already in intensive agricultural production. Oh and by the way the very reason they are "prime bits of land" is generally because of the very fact they were at one time either grassland or savanna and have already sequestered vast amounts of carbon before we plowed them up. In fact they already did what the pseudoscience claims is imposible. 

    I really seriously can't understand why of all places on the web, at least you guys can't get this very important part of climate science right. And please don't just delete of mod clip this post. Because if you'll just answer at least I can go try and find you some good citations to address them.

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    Moderator Response:

    [DB] As you well know, discussions surrounding Savory and his claims belong on more appropriate threads (here or here).

    Off-topic, sloganeering and moderation complaints snipped.

  3. JoeZ: I didn't find it negative, but it is cautionary, and aimed at those who might think that all we need to do is plant trees, or who think that trees can be planted anywhere and thrive. The diminishing of the albedo of the far north by planting there was news to me(mind you, it is still so cold and dry there that few trees would grow).

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  4. So many measures we take such as not using plastic straws or plastic super market bags or even planting trees are feel good measures which simply distract us (or are designed to distract us) from the real problems and their solutions.  Clearly, we simply have to rapidly decrease our use of fossil fuels.  But to do this we have to stop our politicians from doing everything they can to keep us using fossil fuels.  To do this is simplicity itself.  We must stop them receiving money from the fossil fuel industry (and of course, from other harmful vested interests).  Then there is a chance that they will start to act for us, the people who have elected them and who actually pay their salaries and not for their election finceers.

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    Moderator Response:

    [DB] Self-promotional advertising link snipped.

  5. May we hear from an authority on phytoplankton's contribution to oxygen production and its current state in the ocean regarding acidity and shell forming prospects?

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  6. Re: Comment #1 (and others)

    I agree that spending money to stabilize traditional Rainforest management practices and communities would be an excellent investment, far better than monoculture tree planting efforts for the lumber industry or planting pell mell across all biomes and hoping for the best.

    Much of eastern North America has "resprouted" on its own, i.e. pioneering tree species with no particular lumber value have cropped up in many an abandoned fields that were cleared of forest centuries ago during the initial settlement of the United States and much grassland in central North America, at least on the wetter eastern tallgrass prairie sections, have also "gone woody" due to the removal of fire as a management tool to maintain those grasslands.

    I wish foresters across these areas would have some very important conversations on how to manage these otherwise ignored landscapes as part of the equation too. They are not only adapting to climate changes too but could play an important role in transitioning ecosystems in addition to their role of locking up carbon. For instance, what would enable these non-economic woodlands to better provide safe harbor, green corridors and food habitat for the many other species of animals who are having to transition their habitats poleward/up slope/from south to north slopes?  How can these "lower quality" woodlands and non-native grasslands be transitioned into viable green corridors that interconnect highly fragmented native remnants which would otherwise face local extinction as they are surrounded by agricultural/suburban/urban land use patterns?

    So making use of existing vegetation needs to be central to the issue of carbon sequestration by living organism, as they are already there, can no doubt have enhanced carbon fixing properties by tweaking management practices, and  provide additional ecological services.

    And the issues of fragmentation and green corridors for safe passage is a worldwide issue, not restricted just to North America.  So planting a trillion trees should also be done in a way to fit into what is already on the ground, and placed to "fill in the gaps" that exist after looking at the all that is already present.

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  7. By planting trees not only is carbon sequestered from the air but the radiant energy from the sun it is turned into chemical energy rather than thermal energy. While planting trees will produce a darkened landscape they will not respond like a landscape of darkened rocks. Rocks absorb the radiant energy from the sun and heat up radiating in the infrared which is blocked by greenhouse gasses causing global warming. Green plants don't do this. They tend to inhibit global warming.

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  8. Wilddouglasscounty, all of your concerns are intensily discussed and debated here in New England and have been for many years. I've been involved with these debates for decades. I've been promoting a kind of forestry that will produce wood for our economy while having the overall amount of wood in the forests always going up- (with the harvesting being very carefully done) -not as fast as they would with no forestry industry- but it's a tradeoff. I don't think anyone wants to build a home with cement or have plastic furniture or no paper products. But it's a tough fight- there are still logging enterprises which prefer to butcher the forests, there is a huge demand for more housing and many who'd like to continue with urban sprawl, and much forest land is currently being totally destroyed for solar "farms"- about 6,000 acres between 2012 and 2017 according to a recent report by Mass. Audubon.

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  9. WLU, also, trees evaporate vast amounts of water which has a cooling effect.

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  10. Just to clarify- when I said above 6,000 acres of forest destroyed to build solar farms- I should have said just in tiny Massachusetts. I don't have the figures for 2018-2020 but they're popping up faster than before. I did a rank amateur video of the construction of a solar farm behind my neighborhood:

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  11. There are several ways of reducing use of timber. You can build nice sustainable homes with mud bricks or straw bails, and only use timber for the roof framing, so this means we are increasing the amount of timber in a forest (although that must surely reach a limiting factor) but still milling some for the roof. It also means we can expand the area of forests more easily. 

    The trouble is mud brick homes are expensive, because they are labour intensive. I'm not sure how to overcome this.

    The other solution is concrete block homes, again just with timber roof framing. Concrete block is really good, very hurricane resistant, but again is a little bit more costly than timber framed homes, and people go for the cheapest option that has the biggest area, which is timber framing. It is also rather significant in carbon content.

    Given the climate problem one solution might be for governments to give people tax credits if they build with mud bricks. There might not be many takers at first but it might lead to innovations which reduce costs.

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  12. nigelj,

    I suspect wood will always be prefered for building over cement/mud/straw. We can have "wood products" while increasing carbon storage in forests. There is now a movement to build very tall buildings with wood rather than steel using cross laminated timber (CLT): and and many other web sites. It's beautiful, sustainable, and the wood holds carbon.

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  13. I live in Florida.  Many homes and commercial structures here are built using concrete block.  Presumably that is because block is hurricane resistant (there are also a lot of manufactured homes because they are cheap).  You use what works best where you live. 

    Properly managing forests and using the wood to build structures would be a good idea even without cliamte change.  Undoubtedly properly managed forests would yield more money.  I hear that forests in Europe are better managed than forests in the USA.  Does anyone here know the facts about forest management in various parts of the world?

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  14. A significant reason to stop using concrete block is that cement production is a significant source of excess CO2.

    If new materials for making things like concrete blocks sustainably are developed, Then and only Then, should the block building approach be used for new structures.

    Until that sustainable block is developed actual sustainable ways of building need to be employed.

    For tall structures where block building systems are not practical, wood structures are indeed being built as a sustainable alternative to steel and concrete. An example is the recently built 18 storey structure on the University of British Columbia campus.

    However, I think it would be better if all new structures were limited to something like 8 storeys. The shorter structures can have all floors reached by current day fire-rescue ladders. And water services can be delivered to the top without the need for mid-height water reservoir and pump stations (The pressure needed to pump water to the top of a taller building requires impractical pressure resisting water system features at the base of the building).

    Another benefit of shorter buildings is that many people would be capable of climbing up to the 8th floor. That would reduce the power demand for elevators. And reduced energy demand by people is an important part of the changes required for sustainable development.

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