Air Land Water

The AIR we breathe

Despite its critical importance to life on Earth the atmosphere is amongst the least known and appreciated of our global systems. It plays a vital role in the provision of essential ecosystem services, including providing the air we breathe, regulating climate, protecting life from damaging solar radiation, and being integral to the hydrological cycle.

Carbon dioxide and other greenhouse gases are important components of the earth’s atmosphere and their concentrations influence the planet’s climate. Human-caused increases in emissions of these gases, particularly over the last 200 years, threaten the environment and our relationship with it.

Emissions of these gases in the tropics is less than the rest of the world, although the region’s share of global emissions is increasing. Despite accounting for around 40% of the global human population, the tropics only contributes 15% of current greenhouse gas emissions. Emissions in the tropics are greatest in South-East Asia and South Asia, and although increasing rapidly, are still small relative to the rest of the world, particularly on a per capita basis.

Electricity generated from coal and gas is the largest sectoral contributor to carbon dioxide and greenhouse gas emissions. Conversely, electricity generated from low carbon technologies and renewables may be regarded as low impact with regard to climate change effects. How energy is created, distributed and used is an important indicator of future climate change risks and sustainable development.

Since 1980 global electricity production has increased by 150%, with the relative contribution to global generation from the tropics increasing from 7 to 15% in the three decades to 2010. By comparison, the tropics accounted for 23% of all global renewable energy in 2010.

Air pollution has both human and environmental impacts. Air quality indicators reflect a combination of industrial output, economic growth and environmental governance. From a public health perspective an important measure of air quality is the concentration of particulate matter less than 10 micrometres in diameter. Based on this measure, air quality has improved around the world in the 20 years to 2010. However, the extent of improvement is variable and is in part dependent on climatic and geographical constraints. Despite major improvements, no tropical region has yet reached the World Health Organization’s guidelines for healthy air quality.

The LAND that grows our food

Healthy land and soils are the basis of productive agricultural systems. Land degradation refers to the long-term loss of ecosystem function and services caused by disturbance from which the system is unable to recover without help. Land degradation affects the integrity and functioning of ecosystems and, along with climate change and biodiversity loss, is a major threat to the environment, economies and society. It is caused by a number of factors including poor agricultural practices, deforestation, overgrazing and industrial activity. Nearly a third of all land in the tropics became degraded between 1981 and 2003 compared to the global average of 20%. South East Asia had the greatest area of land degradation at 53%.

Most nations rely on agriculture for the majority of their food production and for many nations it is an important part of trade. Increasingly, agricultural land is also used to produce energy such as biofuels. As populations increase, demand for more agricultural land, and increased productivity from existing agricultural land, is rising.

Although the amount of land used for agriculture increased by only 2% in the tropics between 1980 and 2009, productivity of that land increased dramatically. For example, livestock production increased by 89% for cattle/buffalo and 44% for sheep and goats compared with much more modest growth in the rest of the world. Total cereal production in the tropics more than doubled in that time but still lags the rest of the world in terms of both tonnage and yield.

The WATER we drink

The state of the hydrological cycle and water quality are major factors contributing to ecosystem health and human wellbeing. The amount of fresh water available for ecosystems and human society is limited to only 0.3% of total water on Earth. Renewable water refers to the proportion of this available water that is regularly replenished. Efficient and sustainable use of this resource is critical for the maintenance of ecosystem services and human societies.

The tropics has 54% of the world’s renewable water resources of which a quarter is generated outside national borders. Despite having most of the world's water, almost half of the tropical human population was considered vulnerable to water stress in 2010. Current water use patterns are considered unsustainable in many regions. Agriculture accounts for 81% of water withdrawals in the tropics compared with 69% globally. Although tropical rivers are on average less polluted than those in the rest of the world, there is large regional variation, with South East Asia having the highest pollution discharge in the world.


In this State of the Tropics focus essay, Dr Blair Trewin, a climate scientist with the Australian Bureau of Meteorology, explains how climates in the tropics work, how they have changed and what lies ahead.