Completar frases Gap filling - present perfectVersión en línea Read the text about climate change and write the correct form of the verbs in brackets. por Ricardo Brand 1 At the moment , scientists agree that the world's climate 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 alsways ( return ) to the same level . However , since the Industrial Revolution , human beings ( burn ) more and more fossil fuels , such as coal and oil . 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 years ( cause ) global warming . They point out that volcanoes and other natural processes always ( release ) CO2 into the atmsphere , 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 , ( take ) any action .
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