Latest Science Reconfirms:
Trees Are Key To Curbing Climate Change

Jonah Busch

The IPCC says we need carbon capture and storage (CCS) if we’re going to keep global temperatures from rising more than 2°C, but trees remain the only CCS "technology" that can deliver on a meaningful scale. Jonah Busch of the Center for Global Development dissects the latest IPCC report and offers his own meta-analysis of studies on the causes of global deforestation.

This article was originally published on the Center for Global Development’s blog. Click here to read the original.


29 April 2014 | The newly released Intergovernmental Panel on Climate Change (IPCC) report, “Climate Change 2014: Mitigation of Climate Change,” describes the actions that people will need to take if we are to maintain a safe and stable global climate.  Like the two previous IPCC reports (which I have written about here and here), it is based on the collective volunteer work of dozens of top scientists and economists synthesizing the findings of thousands of peer-reviewed articles.

My colleague Alice Lépissier has written here about the IPCC finding that avoiding dangerous climate change is still possible if governments act quickly to set a price on carbon emissions.   So I won’t cover that ground in this blog.   Instead, I’d like to highlight what the IPCC report says about forests.

This IPCC report makes clear that avoiding dangerous climate change by limiting global temperature increase to 2 °C (3.8 °F), as agreed by nations in Copenhagen in 2009, will depend critically on taking carbon dioxide out of the air.   There are two ways to do this. One way is to strip carbon dioxide out of emissions from power plants before it enters the atmosphere, and store it underground.   This technology is called Carbon Capture and Storage (CCS) and is still in early development stages.   Another way to take carbon dioxide out of the atmosphere is by planting trees.   Trees have been sequestering carbon perfectly well for millions of years using photosynthesis.

In a future in which CCS technology becomes available and cost-effective on a large scale, limiting global temperature rise to +2 °C requires reducing deforestation to near-zero by 2030.   Not many models project that it’s possible to limit warming to +2 °C without CCS technology, but those that do require not only stopping deforestation altogether, but reversing it to create a massive terrestrial carbon sink of regrowing forest vegetation by 2030 (Figure 1).



Figure 1. Greenhouse gas emissions by sector in modelled scenarios that limit atmospheric greenhouse gas concentration to 450 ppm CO2eq, with and without Carbon Capture and Storage (CCS) in the electricity sector. Green bars represent carbon sequestration by forests. Source: IPCC WGIII AR5 Figure SPM.7

Since halting and reversing deforestation is so critical to maintaining a safe climate, how can we make this happen?   My colleague Kalifi Ferretti-Gallon and I have been researching this topic for the last year, and I’ll come back to our findings in a moment.   But first, here are three important things to bear in mind about what the IPCC report says about forests:

1.             Net emissions from deforestation are 11% of annual global greenhouse gas emissions.   But the mitigation potential from reducing gross emissions from deforestation is much larger.

The 11% of annual global greenhouse gas emissions (5.4 GtCO2eq/yr) from forest loss is net of forest regrowth. But gross emissions from forest loss are actually much higher than this; about twice as much carbon is released from forest loss as is sequestered due to regrowth. And importantly, forest loss is currently occurring in different regions of the world than forest regrowth.   Accelerating the regrowth of forests in China and India does not diminish the potential to reduce deforestation in Brazil and Indonesia.   So the potential contribution to global mitigation of reducing forest loss is much larger than 11%.

2.             Deforestation emissions comprise the bulk of emissions in some regions.

While net emissions from deforestation comprise 11% of emissions globally, they make up a far larger share of emissions in some countries.   Deforestation makes up more than half of the emissions from Latin America. In Indonesia, deforestation and associated peat degradation represent about three-quarters of emissions. The main way that these countries can participate in slowing climate change is by reducing deforestation.

3.             Research published after the deadline for inclusion in the IPCC report shows that the global pace of deforestation is currently accelerating, not slowing.

The stack of scientific papers published on climate change grows taller with every passing week. So the IPCC necessarily sets a deadline for which scientific papers it can include in its reports.   For this report, papers were only included if they were accepted for publication before October 4, 2013.   Unfortunately, one of the most important scientific papers in years about deforestation was published on October 15, 2013—eleven days after the deadline for inclusion.   This paper by Matt Hansen and his colleagues in Science used satellite data to show that global deforestation rates increased throughout the 2000s (Figure 2).   But the IPCC reports that deforestation emissions are falling, based on a decline in the deforestation rates that countries self-reported to the Food and Agricultural Organization between the 1990s and the 2000s.   IPCC projections of future rates of deforestation also assume falling rates.  If future rates of deforestation are instead projected to stay stable or climb, then even more investment in reducing deforestation is needed to stabilize the climate.



Figure 2. Annual forest cover loss by climate domain in millions of hectares per year, 2001-2010. Source: Hansen et al (2013)


So, coming back to the urgent topic at hand, what drives deforestation and what stops it?   My colleague Kalifi Ferretti-Gallon and I investigate this question in a new CGD Working Paper.   We compiled a comprehensive database of all 117 spatially explicit econometric studies of deforestation published in peer-reviewed academic journals from 1996-2013.   We then present a meta-analysis of what drives deforestation and what stops it, based on the signs and significances of 5909 coefficients in 554 multivariate analyses (Figure 3).



Figure 3. Twenty most commonly studied metavariables’ association with deforestation, organized by sign and significance of coefficients related to that meta-variable. Meta-variables ordered by ratio of negative to positive association with deforestation. For meta-variables in upper case, the ratio of negative to positive observations is statistically significantly different from 1:1 in a two-tailed t-test at the 95% confidence level. Source: Ferretti-Gallon and Busch (2014)

Comparing the relative effects of different drivers of deforestation, we found that:

  • forests are more likely to be cleared where economic returns to agriculture and pasture are higher, either due to more favorable climatological and topographic conditions, or due to lower costs of clearing forest and transporting products to market.
  • timber activity, land tenure security, and community demographics do not show a consistent association with either higher or lower deforestation.
  • population is consistently associated with greater deforestation, and poverty is consistently associated with lower deforestation, but in both cases endogeneity makes a causal link difficult to infer.

Furthermore, we found that promising approaches for stopping deforestation include:

  • reducing the intrusion of road networks into remote forested areas
  • targeting protected areas to regions where forests face higher threat
  • tying rural income support to the maintenance of forest resources through payments for ecosystem services
  • insulating the forest frontier from the price effects of demand for agricultural commodities.

The establishment of international performance-based payments for reducing emissions from deforestation and forest degradation (REDD+) would increase the incentive to successfully undertake any of the above interventions.   That’s why it’s important to learn from large-scale experiments in performance-based finance for reducing deforestation currently taking place in Brazil, Guyana, and Indonesia, and why it’s so critical to scale up performance-based finance for reducing deforestation, as through the Forest Carbon Partnership Facility’s Carbon Fund.

Because without figuring out what mix of policies and finance mechanisms will successfully halt and reverse deforestation, we’re going to sail right through that +2 °C target.

Download the full database here.  


Jonah Busch is a research fellow with the Center for Global Development and environmental economist whose research focuses on the economics of forests and climate change. He can be reached at [email protected].

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