Know better. Do better.

You can call me Al(bedo)

As a climate journalist, people often ask me: shouldn’t we just plant loads of trees?

The simplicity of digging spades into soil and turning landscapes leafy green is very appealing. Trees suck in carbon, so surely we should be planting as many as we can?

If only it were that easy. This week, I spoke to researchers who found that estimates of the climate impact of restoring tree cover are too high - by up to 81%.

That’s because the pros of new planting could be offset by an often unforeseen con: fresh tree cover can change the ability of the earth's surface to reflect sunlight back into space, known as the albedo effect.

For example, if a forest is planted where there was previously just snow cover, the land will reflect less solar radiation. That can negate the climate benefits of trees sucking in CO2.

Overall, trees play a huge role as "carbon sinks", with the world's forests absorbing a net 7.6 billion tonnes of CO2 per year. That's about 1.5 times the annual emissions of the United States.

But because of our friend Al(bedo), the climate benefits or drawbacks of reforestation depend on the location, said the researchers from Clark University, The Nature Conservancy and ETH-Zurich, a Swiss university.

Their conclusion: we ought to be far more selective about where we restore trees. So where should we be planting trees, and why?

That old chestnut

The researchers have pinpointed exactly where reforestation would have a positive or negative climate impact globally. In general, restoring trees in the tropics, such as the Amazon or Congo Basin, will have a large net climate impact whereas tree planting in places like temperate grasslands or savannahs would cause more warming.

"It remains one of the most cost-effective, scalable carbon removal strategies that we have," said Susan Cook-Patton, a co-author of the study and senior forest restoration scientist at The Nature Conservancy, a U.S.-based non-profit.

And there are plenty of other reasons to plant trees, like protecting biodiversity, purifying the air by filtering out pollutants, or boosting mental health.

So don't hang up your spade quite yet.

See you next week,

Jack