Modern agriculture and its beauty to feed billions of people may be one of humanity’s greatest achievements. However, it comes with hidden costs. For example, have you ever considered how much water is needed to provide you with a steak or a salad? It may surprise you.

In a recent study published in the journal Nutrients, scientists from the Commonwealth Scientific and Industrial Research Organization (CSIRO), Australia’s national science organization, took a close look at the diets of 9,341 adult Australians-specifically, their “water-scarcity footprints (水消耗足迹)”.

It turns out that a sweet tooth not only adds to our waistlines but also stresses our water resources.

The water-scarcity footprint is a widely recognized measurement of water consumption. First, it counts the liters of water you used. Then, it looks at the place where the water was used. Using a liter of water in the desert is not the same as using a liter of water in a tropical rainforest. The more scarce water is in your area, the larger your water-scarcity footprint.

The scientists found that the average Australian’s diet had a water-scarcity footprint of 362 liters per day. Snacks and beverages-cookies, cakes, sodas and alcohol-accounted for 25 percent of the water-scarcity footprint. The research also included a glass of wine (41 liters), a single serving of potato chips (23 liters), and a small bar of milk chocolate (21 liters).

Not surprisingly, cutting out snacks would be the top priority if you wanted to lower your own water-scarcity.

Earth’s surface is 70 percent water, but only 2.5 percent of that can be used for drinking or farming. While humanity faces an uphill battle to feed its growing population, climate change is causing droughts and extreme weather in agricultural centers like California and eastern Australia.

By 2030, a world of about 8.6 billion people will need 35 percent more water, 40 percent more energy, and 50 percent more food, according to the United States National Intelligence Council.

Shiny things absorb less heat when left in the sun. This means that if the Earth could be made a little shinier it would be less likely to suffer global warming. Ways to brighten it, such as adding nanoscale specks（纳米级） of salt to low clouds, making them whiter, or putting a thin haze of particles into the stratosphere（平流层）, are the field of “geoengineering”（地球工程）. A small band of scientists which have mostly been using computer models to study the subject. Some of them are now proposing outdoor experiments—using seawater-fed sprayers to churn out particles of the exact size needed to brighten clouds, or scattering sulphur particles（硫粒子） from underneath a large balloon 20km up in the sky.

The scientists hope to understand some of the processes on which these technologies depend, as a way of both measuring their possibility (can you reliably make the proper amount of sea salt brighten clouds?) and assessing their risks (how much damage to the ozone layer might a stratospheric haze do, and how might such damage be minimized?). The experiments would be far too small to have any climatic effects. The amount of sulphur put into the stratosphere by the experimental balloon would be 2% of what a passenger jet crossing the Atlantic emits in an hour.

However, many scientists doubt whether geoengineering experiments have any effects. And some environmentalists say that such experiments reflect the hubris（傲慢）of humans, who believe they can toy with nature.

Geoengineering is not an alternative to relieving climate change by cutting carbon emissions. Even if emissions do start to fall, the cuts will lake decades to have any effect so temperatures are likely to go on rising for some time. The planet is not getting cooler and the pressures on the climate are unlikely to go away. It is therefore not too hard to imagine a world, decades from now, in which emissions are falling but temperatures are rising steeply and the ability to adapt to them has been stretched too far. An additional way to stabilize temperatures might then seem appropriate. Geoengineering offers that possibility.

Now too much CO₂ makes the Earth warmer and warmer, and brings bad effect to people. To save our Earth, a new lifestyle called low-carbon life becomes popular. Low carbon means low energy and no waste. It is necessary for everybody to learn to live a low-carbon life.

To live a low-carbon life, we’d better save as much energy as we can. For example, turn off the lights and TV when you don’t use them, use cold water to wash clothes or dishes; take a short shower and try to take a cold one when the weather gets warm; don’t do the cooking with electricity.

To live a low-carbon life, we should eat less meat. Being a vegetarian can help reduce (减少) one and a half ton of carbon dioxide a year, but keeping animals for food produces even more carbon dioxide than all the cars do in the world.

To live a low-carbon life, we should plant more trees. Trees are very important for us. They can not only produce oxygen for us to breathe and keep the air clean, but also take in the harmful gases from the air. To protect trees we should stop people from cutting down trees and plant as many trees as we can.

If we can keep them a habit in our daily life, the earth will become a safer planet for us to live on.