You are looking at a phase portrait of the publications with keyword from IPCC (the list is displayed when hovering the left part of the screen) in the title of database like pubmed and scopus (you can swich from one to another at the bottom right corner). The diameter of each circle is directly related to the number of publications with keyword in the abstract. The "x" axis is the number of publications while the "y" is the velocity of publications. It has been normalized by the total number of publications for the year "y" (you can swich from one to another at the bottom right corner). A phase portrait does not explicitly express a timeline. So, by clicking on a circle make appears a zoom on the selected keyword phase portrait and its number of publications timeline evolution.