2024年1月27日发(作者：)

森林碳汇(forest carbon sink)

2009-09-23 17:54

碳汇：是指自然界中碳的寄存体。与之相对的概念是碳源，它是指自然界中向大气释放碳的母体。

碳汇一般是指从空气中清除二氧化碳的过程、活动、机制。它主要是指森林吸收并储存二氧化碳的多少，或者说是森林吸收并储存二氧化碳的能力。森林碳汇是指森林植物吸收大气中的二氧化碳并将其固定在植被或土壤中，从而减少该气体在大气中的浓度。森林是陆地生态系统中最大的碳库，在降低大气中温室气体浓度、减缓全球气候变暖中，具有十分重要的独特作用。

有关资料表明，森林面积虽然只占陆地总面积的1/3，但森林植被区的碳储量几乎占到了陆地碳库总量的一半。树木通过光合作用吸收了大气中大量的二氧化碳，减缓了温室效应。这就是通常所说的森林的碳汇作用。二氧化碳是林木生长的重要营养物质。它把吸收的二氧化碳在光能作用下转变为糖、氧气和有机物，为生物界提供枝叶、茎根、果实、种子，提供最基本的物质和能量来源。这一转化过程，就形成了森林的固碳效果。森林是二氧化碳的吸收器、贮存库和缓冲器。反之，森林一旦遭到破坏，则变成了二氧化碳的排放源。

为缓解全球气候变暖趋势，1997年12月由149个国家和地区的代表在日本京都通过了《京都议定书》，2005年2月16日在全球正式生效。旨在减少全球温室气体排放的《京都议定书》是一部限制世界各国二氧化碳排放量的国际法案。它规定，所有发达国家在2008年到2012年间必须将温室气体的排放量比1990年削减5.2%。同时规定，包括中国和印度在内的发展中国家可自愿制定削减排放量目标。在此后一系列气候公约国际谈判中，国际社会对森林吸收二氧化碳的汇聚作用越来越重视。《波恩政治协议》、《马拉喀什协定》将造林、再造林等林业活动纳入《京都议定书》确立的清洁发展机制，鼓励各国通过绿化、造林来抵消一部分工业源二氧化碳的排放，原则同意将造林、再造林作为第一承诺期合格的清洁发展机制项目，意味着发达国家可以通过在发展中国家实施林业碳汇项目抵消其部分温室气体排放量。2003年12月召开的《联合国气候变化框架公约》第九次缔约方大会，国际社会已就将造林、再造林等林业活动纳入碳汇项目达成了一致意见，制定了新的运作规则，为正式启动实施造林、再造林碳汇项目创造了有利条件。

“碳汇”来源于《联合国气候变化框架公约》缔约国签订的《京都议定书》，该议定书于2005年2月16日正式生效。 由此形成了国际“炭排放权交易制度”（简称“碳汇”）。通过陆地生态系统的有效地管理来提高固炭潜力，所取得的成效抵消相关国家的炭减排份额。

“碳汇”的相关概念：碳汇与碳源是两个相对的概念，《联合国气候变化框架公约》（UNFCCC）将碳汇定义为从大气中清除二氧化碳的过程、活动或机制，将碳源定义为向大气中释放二氧化碳的过程、活动或机制。

森林碳汇是指森林植物通过光合作用将大气中的二氧化碳吸收并固定在植被与土壤当中，从而减少大气中二氧化碳浓度的过程。林业碳汇是指利用森林的储碳功能，通过植树造林、加强森林经营管理、减少毁林、保护和恢复森林植被等活动，吸收和固定大气中的二氧化碳，并按照相关规则与碳汇交易相结合的过程、活动或机制。

1997年通过的《京都议定书》承认森林碳汇对减缓气候变暖的贡献，并要求加强森林可持续经营和植被恢复及保护，允许发达国家通过向发展中国家提供资金和技术，开展造林、再造林碳汇项目，将项目产生的碳汇额度用于抵消其国内的减排指标。

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Carbon sinks

What they are and why they undermine the Kyoto Protocol

The scientific basics of the carbon sink concept

Forests as well as soils, oceans and the atmosphere store carbon, which moves among

those different stores over time. Consequently, forests can act as sources or sinks

at different times: Sources release more carbon than they absorb while sinks soak

up more carbon than they emit.

Another important carbon store are fossil fuel deposits. But this particular carbon

store, buried deep inside the earth, is naturally separated from the carbon cycling

in the atmosphere Ð unless humans decide to release it into the atmosphere when we

burn fossil fuels like coal, oil or natural gas. This process has seen greenhouse

gas concentrations in the atmosphere soar to levels more than 30% higher than at

the beginning of the industrial revolution. And through our current greenhouse gas

emissions, we are still adding at least 6 billion tonnes of carbon per year to the

atmospheric carbon cycle, significantly altering the intricate web of carbon fluxes,

and as a consequence, altering the global climate.

The concept of carbon sinks is based on the natural ability of trees, other plants

and the soil to soak up carbon dioxide and temporarily store the carbon in wood,

roots, leaves and the soil.

A flawed concept

The absorption of carbon dioxide by trees and the soil, proponents of carbon sink

credits suggest, would be just as valid a means to achieve emission reduction

commitments under the Kyoto Protocol as cutting emissions of carbon dioxide from

fossil fuels.

Fern profoundly disagrees with this assumption because it overlooks some important

facts:

• For every tonne of carbon stored in a carbon sink, the Kyoto Protocol allows the

release of an additional tonne of carbon from fossil fuel. This substitution has

two important consequences for the atmosphere:

1. Establishing a carbon sink justifies a carbon emission that would otherwise not

have occurred because it would have put the user of fossil fuel over its emission

allowance under the Kyoto Protocol;

2. The amount of carbon available in the active carbon pool (the atmosphere and the

biosphere) increases; this is of key importance because, unlike carbon in fossil

fuels, carbon stored in the biosphere can be released very easily into the atmosphere

through forest fires, insect outbreaks, decay, logging, land use changes or even

the decline of forest ecosystems as a result of climate change. Many of these

activities are beyond government control: more than 50% of the timber exported from

Brazil, Indonesia and Cameroon has been logged illegally and the forest fires in

2000 in the US showed that even technically advanced countries can often do little

to prevent or stop forest fires. Carbon sinks are thus likely to contribute to

increasing long-term atmospheric concentrations of CO2 – the exact opposite of the

intended effect, and a dangerous avoidance of emission cuts which need to take place

now to avoid increasing the threats of climate change to future generations even

further.

• Afforestation – especially afforestation in northern boreal regions – may

accelerate global warming. Climate change is expected to shift Canada’s boreal

forest borders northward and boreal forests are expected to replace the southern

parts of tundra. While this will mean that carbon is removed from the atmosphere

as trees grow, it may not benefit the climate: One of the key factors affecting the

global climate is the ‘albedo effect’, a process, which determines how much

sunlight is reflected back into space and how much warms the earth’s surface. Dark

green forests absorb more sunlight than tundra or farmland, adding to the warming

trend in the boreal if large non-forested areas now covered in highly reflective

snow were planted with trees that shed their snow much faster than the underlying

surface. Similarly in Siberia, it is expected that the positive atmospheric impact

of carbon absorbed by establishing new plantations in the taiga will be diminished

by a reduced albedo effect.

• Measuring biological activities often involves methodologies with high

uncertainties. For many activities, including measuring complete carbon fluxes in

forest ecosystems, estimating and measuring uncertainties of 50% or more are common.

Uncertainties related to the methodology used to determine the amount of carbon

credits from a sink project can thus be bigger than the carbon stock changes measured.

This poses the question of how to verifiably assess and determine how many carbon

credits can be obtained from a carbon sink project.

Yet more negative impacts

Besides the major shortcoming of the concept of carbon sinks from a scientific

perspective, carbon sinks have had and continue to have further negative impacts

on the climate change debate as well as on forests and forest peoples:

• Carbon sinks have dominated the climate change agenda, diverting attention away

from the inescapable need to drastically curb greenhouse gas emissions in

industrialised countries. The focus on carbon sequestration has also stymied any

discussion on how to pro-actively respond to the impacts that climate change is

expected to have on the world’s forests.

• Governmental unwillingness to acknowledge the difference between forests and tree

plantations in the Kyoto Protocol suggests that a substantial part of these

activities would be afforestation and reforestation projects resulting in the

establishment of tree plantations, many of which are likely to be

first carbon sink project that has entered the accreditation process of the CDM is

a tree plantation project in Brazil, where project developers are looking to CDM

carbon credits as a substitute to state subsidies (which were discontinued in the

1990s) for the establishment of plantations.

• Many of the carbon sink projects will be located on lands where forest peoplesÕ

land rights and customary land use have not been recognized to date Ð and in fact

are violated in many cases, as shown in the Fern report Forests of Fear (December

2001, PDF, 1.05MB)]. Yet, forest peoples are not even mentioned in the Climate

Convention. Neither the Convention nor the Kyoto Protocol include any direct

reference to indigenous peoples or forest dwellers. It seems likely under these

circumstances that carbon sink projects will not respect or strengthen forest

peoples’ rights to their lands and natural resources. Evidence of this assumption

surfaced in 2000 when Norwatch, a Norwegian NGO documented the imminent eviction

of local people from lands allocated to a carbon sink project envisaged to provide

carbon offsets for a coal-fired power plant in Norway (Tree Trouble, September 2000,

PDF, 201k).

• Carbon sinks in the CDM will increase the historical carbon debt the North owes

the South. This historic inequality will be superimposed onto the land through the

use of carbon sinks in the CDM: The more greenhouse gases a country emits the more

land it will be entitled to occupy to make up for its emissions. These lands dedicated

to carbon sink projects will be locked up in contractual agreements securing the

area to provide emission rights to the North rather than contributing to meeting

the needs of people in the South.