I have read some Dutch research which showed tha tomatoes grown in Spain had significantly lower CO2 emissions than the same tomatoe grown in the Netherlands, including the transport to the market, which I think was in the Netherlands. I have the paper (in Dutch) lying around somewhere.
The main reason was that the Dutch heat and light their horticultural crop and the Spanish did neither (or much less). The Durch have significantly higher yield per sqm, which is necessary, as their infrastructure (greenhouses, land) is much more expensive. It is slowly changing, as the Dutch are building low energy greenhouses now, but I am not certain if it is fast enough. The greenhouses in place are relatively expensive infrastructure to replace and the profit margins are negligible at the moment.
From an environmental point of view it is tricky, as the Dutch use a lot less pesticides on their horticultural crop than the Spanish do. So it us not all obvious what is better or worse. Although I read recently that in total the Dutch use more pesticides than any other European growers, but I think that is on outside crops, not those in the greenhouse.