Consider this contradiction. Compared with most other professions, scientists are probably better informed and more concerned about climate change. Yet they also fly more than most, generating significant greenhouse-gas emissions. Last month, for example, 31,000 neuroscientists descended upon San Diego for their annual meeting. Even many of those based in the United States flew in.

Researchers should consider what to do about this, because politicians are unlikely to take any action. In countries that have signed the Kyoto Protocol, companies are starting to cut emissions through carbon-trading schemes. But airlines will not join the party, because aviation exhaust gases will lie outside the Kyoto Protocol until at least 2012. That's a problem: the sector generates 3.5% of global emissions, and its contribution is expected to double in the next 15 years.

What should scientists do? Some advice is as well worn as it is tough to take: think about going by train, bike or camel, or whether to go at all. These are not palatable ideas. Conferences are often too distant to reach, except by plane, but good science depends on the exchange of ideas. Nonetheless, it would be worth research groups considering whether they can send fewer members to conferences, and whether more distant and less important meetings can be missed altogether.

One alternative to missing events is to tot up the total emissions incurred by a flight, and invest in small-scale projects to cancel out the emissions. This could involve cutting carbon from other sources, by paying for solar panels, for example, or giving villagers in the developing world stoves that burn more cleanly. The web is teeming with companies that will calculate your next trip's emissions, work out how much it will cost to cut these emissions from other sources (see News Feature, page 268) and invest that amount in selected projects. Bingo — clean, green conferencing.

Some research organizations, such as the Tyndall Centre for Climate Change Research in Norwich, UK, already do this on a routine basis without incurring significant costs. Other institutes should consider following suit. Alternatively, academic societies might choose to add the costs to the meeting fees.

But before doing so, take a good look at the companies that offer to do this ‘carbon offsetting’. The problem is verification. Under Kyoto, companies can invest in well regulated mitigation projects, such as schemes to collect methane from landfill sites. Until offsetting projects are regulated in the same way, there is no guarantee that the firms involved have done their homework. Many offer to plant trees, for example, but forestry is not an accepted emissions-management strategy under Kyoto, partly because it offers no long-term guarantee of soaking up carbon. Trees can be cut down or burnt, especially if local people need them for fuel or economic gain.

To avoid such pitfalls, ask offsetting companies a few questions before investing. How transparent are they? Do they, for example, ask independent scientists to scrutinize their projects? And do they take a truly international outlook? There is little point in restricting investment to schemes in one particular country, as some companies do. Before you invite your colleagues to jet over to your own carbon-neutral conference, make sure that it actually is.