Students at the Calhoun School in New York City have much more than a roof over their heads. They have a rooftop garden, with lush grass, colorful flowers and fragrant herbs. "Green roofs" are sprouting up all over, from schools to city skyscrapers. And roofs aren't the only things going green. Architects are finding all sorts of new ways to build buildings that are easier on the environment. These schools, homes, and offices are called "green buildings".

Normally it takes a lot of energy to run appliances. Too often, that energy comes from burning fossil fuels. So green buildings are designed to do all these things with much less energy. An energy-smart building starts with thick walls. A layer of insulation (隔热材料) traps air to stop heat from passing through. That keeps heat inside in the winter, and keeps heat outside in the summer. This saves energy for heating and cooling.

Heat pumps are another power-saving way to stay comfortable. A ground heat pump moves heat through pipes that run through the ground next to the building. A few feet under the ground, the temperature stays around 10℃ all year round. Water flowing around the pipes helps heat the building in winter and cool it in summer.

Another way to build green is to use recycled materials. That saves the cost and pollution of manufacturing something new. In the Chicago Center for Green Technology, the ceiling tiles (瓷砖) are made of pressed newspaper. The bathroom floors are tiled with recycled glass, and the stall walls are recycled plastic. Builders have found many creative ways to re-use old materials.

As more people become concerned about climate change, more buildings are going green. Green buildings produce less of the gases that warm the planet. City planners like green buildings because they save money. And they are healthier for the people who work and live inside. But you don't need to build a whole new building. Simple changes like shading windows and planting trees can make any home greener—and a better Earth home for us all.

For centuries, scholars have been trying to understand why the Industrial Revolution occurred in Britain around 1750. By studying why similar parts of Britain industrialized at different rates, recent studies show that three factors played the key role: wealth from slave(奴隶) trade, businessmen who stood to benefit from investing, and shortages of lower-skilled workers.

Stephan Heblich and Hans-Joachim Voth analyzed the impact of wealth available from slave trade. They found that riches from slave trade in the Americas flowed mainly to a few cities, such as Liverpool. By the 1830s, these regions had larger numbers of factories and bigger shares of workers employed in various industries.

Investors also needed incentives to industrialize. In early modern Britain, farms were usually very small and most tenant farmers(佃农) just paid fixed rents. Such realities could not encourage landowners to invest in more advanced agricultural machines.

An exception was the churches' land, where such limitations were gone. Between 1536 and 1540, the churches were broken up and their land was sold by Henry VIII. The buyers could farm or rent it on market terms.

A study by James Robinson and Sebastian Vollmer confirmed that areas once owned by the churches were always the pioneers of industrialization. By the 1830s, they had unusually large numbers of workers in different trades, agricultural-machine patents, cotton and grain processing factories. The authors said that these market-based farms encouraged technological advances.

Another factor that has gained support was labour shortages. Bruno Caprettini and Alex Trew studied Britain's wars with France between 1793 and 1815, which led to sharp shortages of lower-skilled farmers and workers. They found that adoption of machines was the greatest in the areas that provided the most servicemen.

The strength of evidence for each of these causes implies that industrialization probably requires a complex mix of conditions. Many important variables are hard to test statistically. But measuring even a few is a promising advance.

In winter, many of us are reaching for more clothes and turning on the heat. Besides wearing a pair of long johns, increasing our food intake can help protect us against severe cold. So what food keeps us warm?

Red meat, such as beef, lamb and pork, is great when you find yourself in cold conditions because it is a fantastic source of iron, which is crucial for circulating your blood. Iron is an important mineral to help carry oxygen throughout your body. People with low iron may notice cold hands and feet or easily become tired. Eating red meat can also supply vitamin B12, which contributes to healthy nerves and a strong immune system.

Oats can keep you warm in winter. It's great thermogenic（生热的）food and is filled with nutrients that release energy slowly throughout the day to keep your body warm. You can start your day with a hot breakfast of oats or other types of porridge. Oats are a great source of whole grains and fiber. In addition to keeping you full and warm, oats are full of other nutrients.

Hot ginger tea can make you feel warm inside on a cold day. Ginger is known to be good for health. It's also a diaphoretic (发汗药), which means it will help your body warm from the inside. Ginger has the nature to produce heat and help blood circulation in our bodies, making it a great source of warmth.

Root vegetables like sweet potatoes need more energy to move through the digestion process, which raises your body temperature. High in vitamin A, vitamin C and potassium (钾), sweet potatoes add fiber and other nutrients to a warm winter meal. Sweet potatoes also have beta-carotene (β胡萝卜素) that is good for eye heath.