IELTS reading practice – Passage one

IELTS reading Practice test passage – Across the planet

Across the planet, forests, wetlands and other vegetation types are being converted to agricultural and other land uses, impacting freshwater, carbon and other cycles, and reducing biodiversity.
The environment adviser Steve Bass says research tells us that “the sustainability of land use depends less on percentages and more on other factors. For example, the environmental impact of 15 per cent coverage by intensively farmed cropland in large blocks will be significantly different from that of 15 per cent of land farmed in more sustainable ways, integrated into the landscape. The boundary of 15 per cent land-use change is, in practice, a premature policy guideline that dilutes the authors’ overall scientific proposition. Instead, the authors might want to consider a limit on soil degradation or soil loss. This would be a more valid and useful indicator of the state of terrestrial health.”
The Earth systems scientist Eric Lambin thinks that “intensive agriculture should be concentrated on land that has the best potential for high-yield crops. We can avoid losing the best agricultural land by controlling land degradation, freshwater depletion and urban sprawl. This step will require zoning and the adoption of more efficient agricultural practices, especially in developing countries. The need for farmland can be lessened, too, by decreasing waste along the food distribution chain, encouraging slower population growth, ensuring more equitable food distribution worldwide and significantly reducing meat consumption in rich countries.”
Over exploitation of groundwater from an aquifer can result in a peak water curve.

Human pressures on global freshwater systems are having dramatic effects. The freshwater cycle is another boundary significantly affected by climate change. Freshwater resources, such as lakes and aquifers, are usually renewable resources which naturally recharge (the term fossil water is sometimes used to describe aquifers which don’t recharge). Over exploitation occurs if a water resource is mined or extracted at a rate that exceeds the recharge rate. Recharge usually comes from area streams, rivers and lakes. Forests enhance the recharge of aquifers in some locales, although generally forests are a major source of aquifer depletion. Depleted aquifers can become polluted with contaminants such as nitrates, or permanently damaged through subsidence or through saline intrusion from the ocean. This turns much of the world’s underground water and lakes into finite resources with peak usage debates similar to oil.[66] Though Hubbert’s original analysis did not apply to renewable resources, their overexploitation can result in a Hubbert-like peak. A modified Hubbert curve applies to any resource that can be harvested faster than it can be replaced.

The hydrologist Peter Gleick comments: “Few rational observers deny the need for boundaries to freshwater use. More controversial is defining where those limits are or what steps to take to constrain ourselves within them. Another way to describe these boundaries is the concept of peak water. Three different ideas are useful. ‘Peak renewable’ water limits are the total renewable flows in a watershed. Many of the world’s major rivers are already approaching this threshold—when evaporation and consumption surpass natural replenishment from precipitation and other sources. ‘Peak nonrenewable’ limits apply where human use of water far exceeds natural recharge rates, such as in fossil groundwater basins of the Great Plains, Libya, India, northern China and parts of California’s Central Valley. ‘Peak ecological’ water is the idea that for any hydrological system, increasing withdrawals eventually reach the point where any additional economic benefit of taking the water is outweighed by the additional ecological destruction that causes. Although it is difficult to quantify this point accurately, we have clearly passed the point of peak ecological water in many basins around the world where huge damage has occurred. The good news is that the potential for savings, without hurting human health or economic productivity, is vast. Improvements in water-use efficiency are possible in every sector. More food can be grown with less water (and less water contamination) by shifting from conventional flood irrigation to drip and precision sprinklers, along with more accurately monitoring and managing soil moisture. Conventional power plants can change from water cooling to dry cooling, and more energy can be generated by sources that use extremely little water, such as photo voltaic and wind.”
The hydrologist David Molden says “a global limit on water consumption is necessary, but the suggested planetary boundary of 4,000 cubic kilometers per year is too generous.”

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