The carbon rainbow we can’t ignore

Understanding the power and limitations of carbon sinks is essential for developing effective climate strategies. In the context of Pakistan’s growing climate vulnerability, leveraging these natural systems is not only urgent but vital.

While terms like carbon sinks, carbon sequestration and carbon farming may sound like specialist vocabulary from climate change discourse, the foundational concepts are introduced early in education. The idea that all life on Earth is carbon-based stems from the basic science of the carbon cycle, a natural process in which carbon circulates through the atmosphere, oceans, soils and living organisms.

Photosynthesis, for example, demonstrates this process clearly. Plants absorb carbon dioxide from the atmosphere and convert it into organic matter, releasing oxygen in return. This process sequesters carbon in plant biomass and soils, thereby maintaining atmospheric carbon levels in check. However, in the last century, human activities have severely disrupted this natural equilibrium.

Since the Industrial Revolution, the amount of CO2 released into the atmosphere has increased by an estimated 400,000 per cent, far exceeding the capacity of natural systems to absorb it. Fossil fuel combustion, large-scale deforestation, intensive livestock farming and land-use change, such as converting forests into agricultural lands, are major contributors to this imbalance.

In a balanced system, much of the carbon released into the atmosphere is absorbed by natural carbon sinks. The most significant natural sinks include forests, oceans, soils and wetlands. These systems capture and store carbon in biomass or deep geological and aquatic layers. However, they vary in their storage capacity and rates of absorption. Deep ocean layers, for instance, are highly effective carbon reservoirs, but the process of transporting carbon to those depths depends on slow oceanic currents, often taking decades or even centuries. In contrast, young forests sequester carbon more rapidly because fast-growing trees compete for light and space.

Despite their importance, the world’s carbon sinks are under severe threat. Excess CO2 absorbed by the oceans has led to acidification, a key factor in coral reef bleaching and marine biodiversity loss. Meanwhile, global deforestation continues at an alarming rate, and an area equivalent to the size of a football field is lost every second. These trends not only diminish the Earth’s capacity to absorb CO2 but also contribute to the further destabilisation of ecosystems and climate systems.

Carbon sinks alone cannot resolve the climate crisis. They were never intended to offset the massive volumes of CO2 being released by modern industrial society. Nevertheless, they remain a crucial part of the solution. According to the Intergovernmental Panel on Climate Change (IPCC), protecting and restoring ecosystems such as forests, wetlands and coastal habitats could sequester up to four gigatons of carbon dioxide annually by 2050.

The concept of the ‘carbon rainbow’ categorises carbon sinks based on the ecosystems in which they are found, using colour as a metaphor to represent different environments: blue, green and brown (or black) carbon. This classification helps illustrate the diversity of carbon storage systems and the need for varied conservation strategies.

Blue carbon refers to carbon stored in oceanic and coastal ecosystems. Oceans circulate approximately 83 per cent of the global carbon cycle. Although coastal ecosystems represent only about two per cent of oceanic area, they are among the most carbon-dense environments on Earth, capable of storing more carbon per hectare than terrestrial forests. Mangroves, seagrasses and salt marshes are especially effective in storing carbon below ground.

For example, mangrove forests in Indonesia are estimated to store up to 3.1 billion tons of carbon per year, nearly three times the annual emissions from global aviation. Pakistan’s Indus Delta, home to one of the world’s largest arid mangrove forests, presents a significant opportunity to scale up blue carbon strategies. However, these ecosystems are increasingly threatened by upstream water diversion, pollution, and unsustainable development.

Peatlands also fall under this category due to their waterlogged conditions, which dramatically slow decomposition and allow vast amounts of carbon to accumulate. Globally, peatlands store up to 44 per cent of the world’s soil carbon. When damaged, however, they release enormous quantities of greenhouse gases, accounting for an estimated five per cent of annual global emissions. Restoration of these ecosystems should be prioritized in climate policy.

Green carbon refers to carbon stored in land-based ecosystems, specifically forests, croplands and grasslands. Grasslands are especially resilient because they store carbon underground, making them less vulnerable to fire and drought than forests. In regions increasingly prone to these hazards, grasslands are being considered reliable carbon sinks. Croplands offer another significant opportunity. Through regenerative agriculture, carbon can be sequestered in the soil, contributing to lower net emissions from the agricultural sector. This approach is central to the European Union’s Green Deal under its Farm to Fork strategy.

Forests, however, remain the largest terrestrial carbon sink. They are estimated to absorb 7.6 billion metric tons of CO2 annually about 1.5 times the annual emissions of the US. Unfortunately, deforestation and forest degradation are threatening to turn even robust ecosystems like the Amazon into net emitters of carbon. In Pakistan, forest cover remains under five per cent, well below the internationally recommended minimum – highlighting the urgent need for reforestation, forest protection and community-based forest management.

Brown or black carbon refers to carbon stored underground over geological timescales, such as in fossil fuel deposits. While these technically act as carbon sinks, they are not viable climate solutions due to the millions of years required for formation. Burning these deposits is the primary source of anthropogenic CO2 emissions. The atmosphere itself, although it holds carbon, is no longer considered a sink because it currently contains far more carbon than it should under natural conditions.

In Pakistan, where climate-induced disasters such as floods, heatwaves and glacial melt are becoming more frequent, restoring natural carbon sinks is both a mitigation and adaptation strategy. Reforestation through scientifically informed and ecologically appropriate initiatives like the Ten Billion Tree Tsunami can contribute significantly to CO2 absorption while enhancing biodiversity and preventing soil erosion. Protection of mangroves and coastal wetlands not only increases carbon storage but also strengthens natural barriers against sea level rise and cyclonic activity. Incorporating sustainable agricultural practices and soil management into national policy could further expand the country’s carbon sink potential.

While carbon sinks cannot shoulder the burden of climate mitigation alone, they offer a powerful and cost-effective complement to efforts aimed at reducing emissions. Harnessing the full potential of the carbon rainbow, blue, green and brown requires coordinated policy, public engagement and cross-sectoral collaboration.

Natural carbon sinks represent a vital, if underutilised, solution in the fight against climate change. For Pakistan, protecting and restoring these ecosystems is more than an environmental goal it is a necessity for sustainable development, economic stability and national resilience in a warming world.