5 . Politicians and the public tend to worry about carbon dioxide (CO₂) emissions (排放) but neglect the effects of cutting methane (甲烷). Actually, dealing with the gas would have a large effect rapidly and at relatively low cost.

Human activity emits far less methane than carbon dioxide, but methane has a heavier impact. Over the course of 20 years, a ton of the gas will warm the atmosphere about 86 times more than a ton of CO₂. As a result, methane is responsible for 23% of the rise in temperatures since preindustrial times. Carbon dioxide gets most of the attention, but unless methane emissions are limited, there is little hope of controlling the climate.

By how much do methane emissions need to fall? Carbon dioxide stays in the atmosphere for centuries, making it hard to reduce its atmospheric concentrations (浓度). By contrast, methane has a half-life of roughly ten years, which means that it degrades quickly. If new emissions can be cut to below the rate at which old emissions reduce, the concentration of methane in the atmosphere will soon fall, slowing global warming. The Intergovernmental Panel on Climate Change estimates that, to keep temperatures between 1.5℃ and 2℃ above preindustrial levels, human methane emissions must drop to 35% below where they stood in 2010 by midcentury.

That is entirely possible. A big step would be to stop millions of tons of methane from leaking out of fossil-fuel infrastructure each year, through pipes with holes, leaky valves and carelessness. The International Energy Agency, a global forecaster, estimates that 40% of methane emissions from fossil fuels, equal to 9% of all human methane emissions, can be got rid of at no net cost for firms. The harder task is to reduce emissions from agriculture, but even here farmers can make use of new ideas, including developing new forms of food for farm animals, and changing how rice is watered.

8 . In late January, returning home from a day in town, my husband and I were greeted by a couple of Willie Wagtails sitting on a hanging basket on our balcony, probably planning to build a nest. Another day away, we came home to find a simple ________ which had started on the hanging basket, right in front of our toilet door. We didn’t have the heart to ________ it, so the “building” ________, with the pair of Willie Wagtails flying in with building materials. Finally after a week, a beautiful nest built with ________ materials was completed.

The next day an egg ________ in their nest, followed by anther two during the week. We were such disturbance to them, having to use the toilet next to their ________.

Two weeks passed and three baby chicks were hatched (孵出). The ________ task began for the parents to find ________ to bring back to their babies. Both Willie Wagtails would fly in and out during the day. It was amazing how ________ the babies were growing.

We were constantly ________ if we came near their nest, and often got our hair pulled just as a ________ to keep our distance. Going to the toilet late one night, I ________ their nest. How lovely it is to see three little ________ and bodies lying neatly side by side, sound asleep, with just their hearts ________ — their little bodies rising and falling with each breath. They were so ________, and I was so lucky to be able to share this special moment.

9 . Over 7,000 species around the world are considered endangered. That number doesn’t even include the plants, animals, and other lifeforms that are listed by some scientists as vulnerable, critically endangered, or extinct in the wild.

The International Union for Conservation of Nature (IUCN) maintains the most-comprehensive list of endangered species around the world. The Red List of Threatened Species, as it’s called, judges each species on five different standards for an in-depth scientific approach. According to the IUCN, an endangered species is one that meets any one of the following criteria (标准): a 50%-70% population decrease over 10 years, a total geographic area less than 5,000 square kilometers, a population size less than 2,500 adults, a restricted population of 250 adults, or a statistical prediction that it will go extinct within the next 20 years.

Though the IUCN’s Red List covers a wide range of what qualifies as an endangered species, it doesn’t quite say how a species reaches those low points. Prepare to feel guilty: the most common factor when it comes to species decline is human intervention. Loss of habitat, the introduction of a foreign species into the environment, hunting, pollution, disease, and loss of genetic variation (基因变异) are all causes of species decline and most often are a result of human activities. Take the bald eagle for example: the rise in human population and urban development of North America limited the animal’s habitat; an increase in hunting the eagles for sport lowered their population size; and the use of the pesticide DDT on farms harmed the animal’s reproductive capabilities.

But even though humans are the number one cause of species decline, classifying species as endangered encourages action to reverse the effects of human intervention. Conservation efforts by the US Fish and Wildlife Service criminalized (使非法) the hunting of bald eagles and the use of the pesticide DDT in the mid- to late 20th century. The effect was positive, as bald eagles have been on the rise and were taken off the endangered species list in 1995.