Climate Science Glossary

Term Lookup

Enter a term in the search box to find its definition.


Use the controls in the far right panel to increase or decrease the number of terms automatically displayed (or to completely turn that feature off).

Term Lookup


All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Home Arguments Software Resources Comments The Consensus Project Translations About Support

Bluesky Facebook LinkedIn Mastodon MeWe

Twitter YouTube RSS Posts RSS Comments Email Subscribe

Climate's changed before
It's the sun
It's not bad
There is no consensus
It's cooling
Models are unreliable
Temp record is unreliable
Animals and plants can adapt
It hasn't warmed since 1998
Antarctica is gaining ice
View All Arguments...

New? Register here
Forgot your password?

Latest Posts


Looking after the right forests benefits the climate

Posted on 6 November 2014 by MarkR

Dr Nadine Unger and other forest-science experts (here and at RealClimate) have recently written about whether saving forests will reduce future climate change. Dr Unger mentions a recent "landmark deal" on sustainable forestry and suggests it's a "bad bet", the others disagree.

I'm convinced that it's a very good bet. If we want to limit global warming, then we have a carbon budget that we can spend, and we can spend this budget by chopping down trees or by doing other things like burning oil and gas. The "landmark deal" aims to keep carbon locked up in forests, clearing space in the budget. Dr Unger argues that planting trees doesn't always help the climate, but her technical points are not really relevant to the tropical forests covered in this particular "landmark deal".

Trees and Temperatures

One way in which trees affect temperatures is that they tend to be darker than grasses or snow. Just like how a black car feels hot to the touch on a bright, sunny day, trees absorb extra heat and warm up. 

This is balanced by how they absorb carbon. Clearing forests releases this carbon (mostly) as carbon dioxide (CO2), a warming greenhouse gas. There are other processes too, and researchers have calculated the total effect that forests have on temperatures. Dr Unger mentions the surprising result that planting trees in colder areas can boost warming (e.g. Bonan et al., 2008).

However, tropical forests are very dense. Powered by bright sunlight year round and fuelled by heavy rainfall, they suck up enormous amounts of carbon. There's wide agreement that they have an overall cooling effect, and one of Dr Unger's own references (Jackson et al., 2008) states straight up that "Tropical projects—avoided deforestation, forest restoration, and afforestation—provide the greatest climate value".

In general, one of Dr Unger's points is that in many developed countries, like the US and UK, planting trees isn't going to help reduce global warming. This is probably true, but not relevant for the "landmark deal" under discussion. This is about Reducing Emissions from Deforestation and Forest Degradation (REDD+) in Developing Countries (more details are in a note that I researched and wrote for the UK Parliament).

Here's a map of countries doing REDD+ projects. It's dominated by tropical forests in countries like Brazil, Peru and Indonesia.

Figure 1 Map of countries with current REDD+ projects, darker shade means that the country has more projects. Modified from this map, produced by CIFOR.

Forests and Fuels

The UN has a target to prevent global warming from going above 2 C (3.8 F). From 2011, the entire remaining budget was about 1,100 billion tonnes of carbon dioxide (IPCC, 2013).

We expect to release about 400 billion tonnes of CO2 from forests this century (Gullison et al., 2007), meaning everything else can release 700 billion tonnes of CO2. However, successful REDD+ could save forest carbon and boost the "everything else" budget by more than 50% to 1,100 billion tonnes of CO2.

However, the International Energy Agency says that there are already almost 3,000 billion tonnes worth of CO2 in "proven reserves" of coal, oil and gas, and we're looking for more (World Energy Outlook 2012). In the fight against climate change, REDD+ is a hefty punch, but we don't score a knock out until we decide to leave lots of fossil fuels in the ground. These would be the "unburnable" fossil fuels.

Why not think of forests in the same way? As long as they're intact or well-managed, then they store lots of carbon just like an oil field or coal seam. Instead of destroying rainforest we could destroy some oil fields instead. Regardless of what we do though, at least two-thirds of reserves are going to have to stay in the ground. At least, until industrial scale carbon capture and storage (CCS) is demonstrated and funded on an enormous scale.

Investing in Tropical Forests is a Good Bet

All forests can provide enormous benefits. They keep productive soils around, they reduce flood damage, support important plants and animals and they are beautiful. These are good reasons for investing in forests, but the climate picture is more complex. Dr Unger points out that in some areas, planting a forest isn't going to have much climate-cooling effect. This is important if you're thinking about buying carbon offsets in temperate forests. But when talking about the "landmark deal" on REDD+, this is irrelevant. That deal is about tropical forests where there's a consensus that they reduce global warming.

REDD+ is technically very difficult to set up and make sure that it is clean and fair. But in scientific terms it's a very good bet for helping to reduce future global warming.

If we're going to hit the UN climate targets to limit global warming, and if REDD+ doesn't work, then we'd have to leave more fuels in the ground. If REDD+ does work, then we can risk burning those extra fuels. In fact, it buys us about 10 years of current fossil fuel burning. That leeway is worth having, but it's still absolutely necessary to slow down fossil fuel burning. Either way, the carbon from at least two-thirds of fossil fuel reserves has to stay in the ground.

NOTE: The author's POSTnote note was produced as part of a temporary fellowship funded by the UK's National Environment and Research Council (NERC), and this post is entirely personal opinion and doesn't represent NERC or the Parliamentary Office of Science and Technology.

0 0

Printable Version  |  Link to this page


Comments 1 to 5:

  1. Many of the darkest green countries with the most forest-saving projects are also places that have some of the highest bio-diversity in the world. Even if GW weren't the global crisis that it is, these would still be vitally important projects to carry out. Too bad there aren't more of them in Africa.

    0 0
  2. More on Africa: Too bad, because particularly in many parts of Sub-Saharan Africa there are many areas of high bio-diversity that are in need of preservation.

    Preventing the loss of forest there may also have helped prevent (or made less likely) the recent outbreak of Ebola. Deforestation has been tightly linked to deforestation in the region, since the forest animal vectors are more likely to end up where more people are, and so get eaten leading to new outbreaks.

    0 0
  3. There are loads of benefits that rainforests provide, but I didn't want to get bogged down in that discussion with this post. 

    In principle, REDD+ is about paying for carbon alone, on the basis that this is good climate policy. I think that this is very well-jusified scientifically, and Dr Unger's piece could be interpreted as a claim that it isn't. 

    In principle, the other wonderful advantages of rainforests, such as biodiversity, providing new chemicals for medicines and stopping precious productive soil from washing away would also be worth paying for. But if I talked about that, then the blog post would have gone on and on!

    0 0
  4. That's what I figured. But that's what comment sections are for--things you couldn't get to in the main article (and of course other things, sometiems) aren't they? '-)


    0 0
    Moderator Response:

    [JH] The purpose of the comment threads on the SkS website is clearly articulated in the introductory paragraph of the SkS Comments Policy, i.e., 

    The purpose of the discussion threads is to allow notification and correction of errors in the article, and to permit clarification of related points. Though we believe the only genuine debate on the science of global warming is that which occurs in the scientific literature, we welcome genuine discussion as both an aid to understanding and a means of correcting our inadvertent errors.  To facilitate genuine discussion, we have a zero tolerance approach to trolling and sloganeering. 

  5. wili @4, for off topic but related comments, it is generally easy to find an article on Sks where they are on topic, make the post there and link back on the thread which initially started the thoughts.  If all else fails, almost everything is on topic in the weekly digest posts (not the news digests).

    0 0

You need to be logged in to post a comment. Login via the left margin or if you're new, register here.

The Consensus Project Website


(free to republish)

© Copyright 2024 John Cook
Home | Translations | About Us | Privacy | Contact Us