What is the relative climate damage of methane-burping cows compared with air travel?

Air travel (aviation) contributes about 2% of global carbon emissions. Cows account for about 6%.
Energy production is by far the largest source of carbon emissions, so reducing fossil fuel use is the biggest priority, but because transport uses fossil fuel, that is also a sector that will need to change significantly.

In Australia, cows account for about 10% of carbon emissions, so more than the global figure, because Australia does produce a lot of beef. In Australia cars are responsible for about 10% of emissions as well, while aviation sits around the same level in Australia as globally, at 2%.

So reducing air travel, car travel and red meat consumption are all powerful ways to fight climate change, but reducing our reliance on fossil fuels and switching to renewable energy wherever possible is the biggest area to improve.