4.2. Permafrost vulnerability
According to Figure 4, the ground temperature of the entire QTP permafrost is relatively high. In order to analyze the vulnerability of the QTP permafrost to climate warming, the permafrost region with MAGTs ranging from -0.5 to 0.5°C was extracted (Figure 10). According to the permafrost stability classification (Cheng and Wang, 1982), permafrost in this range is classified as unstable region. It can be observed that 0.49 × 106 km2 of the permafrost area over the QTP is in danger at present, which accounting for 37.3% of the maximum permafrost area. This unstable permafrost primarily distributed in the transition region of permafrost and seasonally frozen ground.
As a result of the global warming and increased anthropogenic activity, the QTP has experienced an approximately 3-fold warming increase over the past 50 years (Wan et al., 2018). Under the influence of this accelerated warming, the permafrost region adjacent to the seasonally frozen ground is becoming increasingly fragile (Qin et al., 2017). This part of the permafrost is generally in the process of ice-water phase transformation. A comparison with Figure 6, reveals that this region is consistent with the areas in which permafrost will disappear under future RCPs, but it also greatly affected by the local ground ice content, underlying surface types, and other related factors (Nelson et al., 2001; Yang et al., 2010c).
The Qinghai-Tibet Engineering Corridor (QTEC, the region that contains the Qinghai-Tibet Highway and Railway, pipelines, electric transmission lines, and so on) is an important conduit connecting mainland China and the QTP. Under the influence of intensifying global climate change and frequent human activities, the ecological environment along the QTEC is fragile, and the permafrost in the QTEC has degraded significantly and the alpine ecosystem is facing new challenges (Niu et al., 2018). Based on Figure 10, the statistical results show that 757 km of the QTEC crosses through the permafrost region (at its maximum extent), accounting for nearly 40% of its total length (from Xining to Lhasa). Of this, approximately half of the QTEC faces the risk of the permafrost disappearing, and the other half may experience varying degrees of permafrost degradation in the future. This will result in huge economic losses and threaten associated infrastructures along the QTEC.
Recent studies have shown that several cryosphere tipping points are dangerously close (IPCC, 2019), and the permafrost in the Arctic has begun to thaw irreversibly and release carbon dioxide and methane, but the inevitable effects could still be mitigated by reducing greenhouse gas emissions (Lenton et al., 2019). The stability and resilience of the QTP permafrost is in peril. We should take urgent action to reduce greenhouse gas emissions, and put them as the priority of the present and future work. In order to effectively mitigate the degradation of permafrost, all the emission reduction measures should be reflected in words even in actions.