Climate Change (Present Perfect vs Past Simple Review)

1. Complete the following text using Past Simple or Present Perfect:

Climate Change




At the moment, scientists agree that the world's climate _______________ (become)  warmer over the past 50 years, but they disagree about the causes. Some believe that human activities ______________ (cause) climate change. They argue that for 1.000 or 2.000 years before 1850, when records ____________ (begin),  the temperature was more or less stable. Short warm or cold periods _____________ (occur) during that time, but the climate always ___________ (return) to the same level.

However, since the Industrial Revolution, human being ____________ (burn) more and more fossil fuels, such as coal and oul. In 1800 the atmosphere ______________ (contain) around 280 parts per million of carbon dioxide (CO2). Since then there _________ (be) an increase of about 31%. This extra carbon dioxide ______________ (raise) the world's temperature because of the greenhouse effect.

Other scientists disagree that human activities over the past 50 years _____________ (cause) global warning. They point out that volcanoes and other natural processes ______________ (always/ release)  CO2 into the atmosphere, and that human activity _____________ (contribute) a rise in CO2 of only three per cent.

In 1999, 156 countries _______________ (sign) the Kyoto protocol, part of a United Nations agreement on climate change, which ______________ (come) into force in 2005. They _______________ (agree) to reduce their emissions of CO2, and other greenhouse gases, although so far, some countries, such as the USA and Australia, _______________ (not/ take) any action.

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