Section 1: Atmospheric Photochemistry and Air Pollution

What is “sustainability”? Is it the same thing as taking action on climate change?

Climate action is just one form of sustainability—a concept that asks us to see the big picture of what we are taking from the Earth, and how our actions affect future generations.

Which is more likely: electric airplanes or hydrogen-powered airplanes?

For long-range flights with many passengers, liquid fuels like hydrogen are probably our best bet.

Is there a danger that pumping liquid carbon dioxide underground could have the same negative impacts as fracking?

Pumping carbon dioxide deep underground can cause earthquakes under certain conditions, but there are ways to prevent this.

With low-carbon technologies improving so fast, does it sometimes make sense to wait to invest in new infrastructure?

It can make sense to wait for low-carbon technology to improve in efficiency and cost, but to slow climate change we must balance what makes economic sense with what reduces emissions the fastest

What is the ideal level of carbon dioxide in the atmosphere for human life?

Atmospheric CO2 levels of between 280 and 350 parts per million created the climate that let humanity build and feed the modern world. The farther we get from those levels, the more we run the risk of disturbing that balance.

If cities require new buildings to use 100% electric heat, will that raise or lower their greenhouse gase emissions?

Electric heating can cause a short-term rise in emissions in areas that get their electricity from fossil fuels. But without electric heat, we can’t get greenhouse gas emissions to zero

Why did the IPCC choose 2°C as the goal for limiting global warming?

Scientists and policymakers have long agreed that global warming beyond 2° C above the pre-industrial average would pose large and escalating risks to human life as we know it on Earth, and governments have used that number as an organizing principle.

Why do we compare methane to carbon dioxide over a 100-year timeframe? Are we underrating the importance of methane emissions?

This greenhouse gas is short-lived but has far greater heat-trapping potential than CO2. The more concerned we are about global warming over the next 10 or 20 years, the more emphasis we have to put on cutting methane emissions.

Why do some people call climate change an “existential threat”?

The phrase can refer to a literal threat to humanity’s existence, but also to the danger that unchecked climate change can pose to our ways of life and place in the natural world.

Which parts of the planet are warming the fastest, and why?

The earth’s largest land masses and its north and south poles are warming the fastest, mainly because of differences in how these areas reflect energy from the sun.