Already it felt as though the earth would never warm again.

If the sun generates more light, the Earth will warm.

At that time, the earth was warming from its most recent ice age.

The line you quote doesn't state he questions if the Earth is warming.

Where does that leave the people who were raising questions about whether the Earth was really warming?

Whether the earth has warmed and cooled isn't the issue.

There is agreement among the scientific community that the earth has warmed in the last century.

Increased levels of greenhouse gases must cause the Earth to warm in response.

Anyway, how can they be sure that the earth has warmed in the last few centuries?

It was reported in 2002, that the earth had warmed approximately 0.6 C over the past 100 years.