One of the great construction cons, as I've posted previously, is the way in which we account for CO2. This isn't an argument about AGW or the effects of CO2, it's a matter of crooked accounting. Bloomberg's new 'eco' building in London actually cost something like 250,000 tonnes of CO2, but if the steel was made in China and the cement in Thailand (as is very common) only a fraction of that CO2 cost will appear on the UK's national CO2 total. CO2 is accounted for at place of production rather than consumption.
The result of increased steel tariffs imposed by President Trump will doubtless be Chinese steel producers with a surplus of steel, which they'll seek to dump on world markets, including the EU. The more steel the Chinese dump on Europe, the lower Europe's CO2 emissions under the crooked accounting system.
Every cloud has a silver lining - that Mr Trump will allow us to claim a significant reduction in CO2 emissions will no doubt be of great pleasure to those who believe such measures have any worth at all.