Find in Library

<p>Understanding the dominant climate forcings in the Pliocene is crucial to assessing the usefulness of the Pliocene as an analogue for our warmer future. Here, we implement a novel yet simple linear factorisation method to assess the relative influence of <span class="inline-formula">CO₂</span> forcing in seven models of the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2) ensemble. Outputs are termed “<span class="inline-formula">FCO₂</span>” and show the fraction of Pliocene climate change driven by <span class="inline-formula">CO₂</span>.</p> <p>The accuracy of the <span class="inline-formula">FCO₂</span> method is first assessed through comparison to an energy balance analysis previously used to assess drivers of surface air temperature in the PlioMIP1 ensemble. After this assessment, the <span class="inline-formula">FCO₂</span> method is applied to achieve an understanding of the drivers of Pliocene sea surface temperature and precipitation for the first time.</p> <p><span class="inline-formula">CO₂</span> is found to be the most important forcing in the ensemble for Pliocene surface air temperature (global mean <span class="inline-formula">FCO₂=0.56</span>), sea surface temperature (global mean <span class="inline-formula">FCO₂=0.56</span>), and precipitation (global mean <span class="inline-formula">FCO₂=0.51</span>). The range between individual models is found to be consistent between these three climate variables, and the models generally show good agreement on the sign of the most important forcing.</p> <p>Our results provide the most spatially complete view of the drivers of Pliocene climate to date and have implications for both data–model comparison and the use of the Pliocene as an analogue for the future. That <span class="inline-formula">CO₂</span> is found to be the most important forcing reinforces the Pliocene as a good palaeoclimate analogue, but the significant effect of non-<span class="inline-formula">CO₂</span> forcing at a regional scale (e.g. orography and ice sheet forcing at high latitudes) reminds us that it is not perfect, and these additional influencing factors must not be overlooked. This comparison is further complicated when considering the Pliocene as a state in quasi-equilibrium with <span class="inline-formula">CO₂</span> forcing compared to the transient warming being experienced at present.</p>