Be honest...if it were said and could be proven beyond any reasonable doubt that we had 300 years then how many would change their position? People would rationalize that they, their children and grandchildren will all be long dead and gone so why should they worry about it.
The overall average temperature change over the last 100 years has been slightly over 1 degree. Not sure 1 degree of change would be noticed given the random nature of weather. It isn't the extremes high or low but the averages over time that matter. It's going to be difficult to observe by walking outside especially in temperate climates like we have here in Ky. But go to the polar ice caps where they form over decades and observe that they are noticeably smaller.
"The National Oceanic and Atmospheric Administration has said that 2016 set a new record high annual temperature (along with 2005, 2010, 2014, and 2015) and marked “the 40th consecutive year (since 1977) that the annual temperature has been above the 20th century average.”
Last year continued that trend. At likely the third warmest year on record, 2017 marked the 41st consecutive year above the 20th century average."
It doesn't help anyone when the idiot in the White House says in an interview on tv; "The ice caps were going to melt, they were going to be gone by now, but now they’re setting records, so OK, they’re at a record level." Jan 28, 2018. When asked to back the claim...Trump doesn’t specify whether he means record high ice cap levels or record low, though from the context he suggests high. He also doesn’t specify which ice caps he’s referring to or what time periods. We reached out to the White House for clarification and support for Trump’s claim. The White House has yet to get back to us. And good luck ever getting an answer. The same person probably advised him on the polar ice caps as advised him on "the biggest tax cut", "biggest landslide victory", that his job approval ratings are "better than most"...that the Russians didn't interfere in the election or that there was massive voter fraud. Not true, not true, not true, not true and not true.