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Alarm bells sounded when research suggested the possibility that nearly one in every four English soccer stadiums could be partially or completely flooded in the near future due to climate change and extreme weather events.

Some research even predicted that by 2050 almost half of the cities that once hosted the Winter Olympics would not be able to do so again for lack of snow and ice.

Also, the US Open Tennis Championships organizers implemented an “extreme heat policy,” having mandatory short breaks for players to cool down during matches, after a few quit their matches due to extreme heat.

As more sports are affected by climate change, concerns are growing.

that nearly one ... events는 the possibility와 동격을 이룬다.

Some research even predicted that by 2050 almost half of the cities that once hosted the Winter Olympics would not be able to do so again for lack of snow and ice.

that once hosted the Winter Olympics는 half of the cities를 수식하는 관계절이다.

do so는 앞에서 언급된 동작이나 행동을 대신하는 역할을 하며, 여기서는 host the Winter Olympics를 대신하고 있다.

having mandatory … during matches는 분사구문으로, the US open Tennis Championships organizers의 행동을 부연 설명한다.

After the event has ended, in addition to the significant amount of trash that needs to be disposed of, the effects those people caused and the emissions generated from their travel continue to have a lasting negative impact on air quality.

that needs to be disposed of는 trash를 수식하는 관계절이다.

those people caused는 the effects를 수식하는 관계절로 앞에 목적격 관계대명사가 생략되었다.

generated from their travel은 the emissions를 수식하는 분사구이다.

It turns out that participants do not make bad impressions but make better impressions than they think.

It은 형식상의 주어이고 that 이하가 내용상의 주어이다. ‘A가 아니라 B’의 뜻인 not A but B 구조가 사용되어 make bad impressions와 make better impressions than they think가 but으로 대등하게 연결되어 있다.