Recent findings suggest climate change in Greenland may be approaching a tipping point, beyond which amplifying feedbacks could lead (probably over centuries) to complete melting of the ice sheet, raising sea level by about 7 meters.
In June, a team of glaciologists led by Jason Box predicted that we would see melting across 100% of the ice sheet’s surface area in summer within a decade (Box et al., in press).
They drew that conclusion from data on the Greenland ice sheet’s surface reflectivity, or “albedo”, showing the surface has gotten darker over the last 12 years. A darker surface absorbs more heat, leading to more melting, causing albedo to decrease further, and so on in a vicious circle.
This month, at the height of the melt season, Greenland’s albedo has fallen far off the charts [see Figure 1].
Then NASA satellites recorded a startling abrupt acceleration of melting over just four days. On 8 July, about 40% of the ice sheet’s area had surface melt. By 12 July, surface melt had spread to no less than 97% of the area, penetrating all the way to the centre of Greenland, three kilometers above sea level [see Figure 2].
...The extraordinary events of recent weeks are cause for concern when considered in the context of Greenland’s ice melting at an accelerating rate for the last decade, losing more than 2 trillion tonnes in total.
There is broader evidence that no significant cushion remains between today’s climate and a dangerous level of warming.
In the last interglacial age 125,000 years ago, called the Eemian, global temperature was only ~1°C warmer than preindustrial, ie. only a couple of tenths of a degree warmer than today (Hansen et al., in press).
Yet the poles were several degrees warmer, there was no summer sea ice in the Arctic, and multiple studies using different methodologies (Kopp et al., 2009; Dutton & Lambeck, 2012) say sea level was 6-9 meters higher (meaning at least partial melting of the Greenland and/or West Antarctic ice sheets).
All this points to the conclusion we may already be getting close to a dangerous level of global warming.