By Roger Harrabin
BBC Environment Analyst
Can Madonna save the planet? What exactly is the relationship between her and Al Gore? Can you calculate the CO2 emissions from a pop concert?
The answers to these and a few other questions will be a little clearer by Sunday.
Let's unpick question one - does the planet need saving?
The Intergovernmental Panel on Climate Change (IPCC) says it does.
Even the White House signed up to the IPCC's "unequivocal" finding that emissions from mankind have been driving most of our recent climate change.
They and all governments agree that we need to move to a lower-carbon model of progress, though they disagree over the level of urgency.
Can Madonna provoke the change? Of course not, but she and the other high-rolling artists singing their own song of the earth at stadiums around the world can certainly bring public attention to the issue.
In the UK, people are saturated by climate change messages, but still (according to Mori research this week) wrongly think that scientists are locked in major debate about its causes.
The American public know less about the climate - and in South Africa, which hosts one of the concerts, climate change is barely mentioned, even though Africa is predicted to suffer most from it.
So Madonna and her mates can raise the profile of the planet.
The concert will be peppered with handy hints for greening your lifestyle, but subsequent CO2 cuts will probably prove insignificant compared with the message the concerts will send to political leaders, legitimising climate change as an issue of public concern.
In modern democracies politicians only go as far as they think their electorates will let them, so the Gore extravaganza will have some political impact.
Madonna will perform at the London concert in Wembley Stadium
Question two is what about the emissions?
The concert organisers have gone to great lengths to try to minimise emissions, but admit that for all their efforts they will probably reduce CO2 by no more than 20-25% less than the average concert. Modern lifestyles pollute.
That said, they are trying to set a new standard for green events.
Among the steps being taken are: all electricity that powers the shows will be from renewable sources, either through utility-supplied renewable energy, biodiesel generators or renewable energy credits.
The biodiesel will not come from rainforest land. Energy-efficient lights will be used where possible. Travel for staff and artists' air travel will be carbon off-set.
You could pick holes in all this.
Off-setting air travel is controversial, although many environment analysts think it is better than doing nothing.
Concert proceeds will go to the Alliance for Climate Protection
Biodiesel from crops arguably puts up food prices and will never supply more than a fraction of our transport needs.
But what organisers have modestly (or mistakenly) failed to estimate is the amount of emissions that will be saved if millions of people stay at home in front of the telly watching Gore and Madonna rather than taking a drive for Saturday night out.
There may be many scientific uncertainties over how much the climate will change and over what time frame, but the organisers have no doubt calculated that every kilogram of CO2 generated round the world by the concerts will be well spent if it jolts politicians to respond with a little more urgency to the warning the scientists are sounding.