Deep-time perspectives of 20th century to early 21st century trends in the atmosphere-ocean system indicate the glacial-interglacial history of the last ~800 kyr is dominated by non-linear to abrupt climate shifts, including irreversible tipping points, driven by orbital insolation pulsations (~40-60 Watt/m2) triggering feedbacks from ice melt/water interaction and greenhouse gas (GHG) release. The current rate of GHG (CO2, CH4, N2O, ozone) rise at ~2 ppm CO2/year is the fastest recorded in the geological record, with the exception of events associated with mass extinction of species. This rate is higher by a factor of ~5 than that associated with the Paleocene-Eocene thermal event (PETM) when a release of ~2000 billion ton carbon (GtC) was triggered an abrupt greenhouse event of ~5oC (deep ocean temperature) on a few decades time scale, lasting up to 10,000 years. Temperature rise rates during the 20th century and since ~1975 exceed those of glacial terminations by factors of near-30 and are similar to rates of the ~1470 years-long intra-glacial D-O (Dansgaard-Oeschger) cycles, where sharp temperature rises occurred in Greenland (~6 – 8C in few decades), extending to lower latitudes. Current atmospheric radiative forcing reached over 50 percent of the ~6 Watt/m2 forcing of the last glacial termination. Glacial termination events were preceded by low-variability lulls, followed by a response to peak radiative through irreversible shifts between distinct climate states. Current GHG forcing level of +3.2 Watt/m2 since 1750, driven by carbon emission, fires and land clearing, is currently masked by the albedo enhancement effect of emitted SO2 aerosol, estimated as -1.6 Watt/m2. At 393 ppm CO2 and 470 ppm CO2-equivalent, the atmosphere/ocean system is tracking toward the ~500±50 ppm CO2 upper stability limit of the Antarctic ice sheet. The currently rising GHG level would, in part, buffer the atmosphere in relation to solar orbital forcing, inducing a near-permanent El-Nino state and reaching conditions analogous to those of the Pliocene and mid-Miocene, when mean global temperatures were +2 to +4oC above the present, continental ice sheets were about half the present and sea levels were ~ +20 to 40 meters above present. Depending on the level of future GHG rise, elevated temperatures may delay or cancel the next glacial cycle.