Apply a worldwide carbon tax to all emissions, which gradually increases year by year. Knowing that flying will become a less and less viable business model over time, governments and investors will begin on alternative investments in infrastructure and novel technologies.

For overland travel: trains.

For across oceans: probably also trains, possibly in tunnels.

Benefits to this approach:

• Actually reduces carbon emissions instead of moving them around.
• Doesn't tell the individual to stop flying or eating steak. Leaves it up to them to decide which carbon emissions they value most.
• Doesn't pretend to be omniscient and perscribe solutions. Instead lets everyone in the world solve the problem creatively.
• Creates a market incentive to accellerate the production of alternative technologies.

Most likely what would happen is that high speed rail would see a big boom immediately as governments looked for ways to reduce intra-country transit costs. Overseas flights, which are quite a bit rarer, would probably stay stable for several years (though with a fair amount of griping about the increased cost of flying). However, as time went on we would also expect to see overseas flights drop significantly. Businesses would prefer teleconferencing to sending delegates overseas for small matters. People would vacation overseas less frequently, instead staying on their own continents. Possibly there is a new industry - high speed sailing cruise ships - which would transport people across oceans at slower speeds for their vacations. Someone might invent better forms of carbon-neutral energy storage to make air travel more feasible again. Otherwise, nations start building undersea tunnels to connect rail lines across oceans.