Recent analyses of ice cores show that carbon dioxide levels were ________ lower over the last 600,000 years than they are now.

The problem of global warming is ________ as one of the most serious environmental problems of our time.

Not only ________ this planet, but we have completely wiped out hundreds of species.

The last pied raven was shot in the late 1940s. The species ________ saved but people were too ignorant.

The only way to stop overpopulation is to reduce the birth rate. This ________ a question of whether people have a right to have children.

If you want to save money and the environment, try ________ less detergent, shampoo and other cleaning materials.

It's by sorting and recycling our garbage ________ we can save the planet.

Fortunately, ________ no longer on the list of endangered species.

Mike and Debbie used to be good friends but they fell ________ over the issue of climate change. Mike believes it's just a scam, a tool being used to make certain individuals rich.

The idea of using public transport instead of driving is nice but it's not what most people are willing to put ________.

According to S. Edwards, a million species ________ by 2050.

Despite everything we hear from TV and the radio, people ________ to destroy the planet.

According to research, forests are dying twice ________ they did 20 years ago because of climate change.

If you'd seen Al Gore's movie “An Inconvenient Truth”, you ________ a lot differently about the issue of global warming.

I had ________ success with my conservation project in my company. It was dismissed as being too costly.