We're at 387 ppm CO2 but 455 ppm CO2e. CO2e is carbon dioxide equivalents. Nitrous oxide and other gases contribute to climate change as well but unequally. Listing CO2e takes their different contributions into account and lists the amount of CO2 the sum of all greenhouse gases would be. This is the more commonly used definition.
To add more confusion to the mix CO2e can also be defined as the net effect of all forces (both warming and cooling) in how much CO2 they equal. Using this definition current levels are 380 ppm.
The people who list the target of 450-500 ppm CO2e are using the net effect definition. It's unclear which definition this author is using when he lists current levels as 430 ppm since the two definitions yield either 380 ppm or 455 ppm CO2e. I don't know if he's 25 ppm too low or 50 ppm too high. Since his current level is listed as 430 which is close to 455 than 380 I assume he is using the greenhouse gases sum definition. It is incorrect to use one definition at one point and the other definition at another. This gaff suggests he may not know and/or understand the different definitions of CO2e.
John Thornton