0.5 Degree: A Turning point

<p>Although the Caribbean region is considered amongst the most vulnerable to the impacts of climate and climate change, there are very few regional studies or studies matching the regions small scale and size that evaluate or quantify the impacts of these future changes.  The absence becomes even more stark when the long-term temperature goals (LTTGs) of 1.5°C, 2.0°C and 2.5°C above pre-industrial warming levels are considered. By selecting, validating and downscaling a subset of the Hadley Centre’s 17-member Perturbed Physics Ensemble for the Quantifying Uncertainty in Model Predictions (QUMP) project, future changes for both the LTTGs as well as mid and end of century are evaluated, for the entire Caribbean and its six (6) sub-regional zones. Showing distinct and significant sub-regional variations, on average the Caribbean was found to be 2.1°C (>4°C) warmer and 40% (70%) drier by mid-century (end of century). Analysis of the LTTGS shows that the region surpasses lowest target, 1.5 °C, before the end of the 2020’s and experiences progressive warming that spread equatorward as successive thresholds are attained 2.0°C (2030’s) and 2.5°C (2050´s). The far western, the southern and the eastern Caribbean are found to be up to 50% drier at 1.5°C, with intensifications noted for changes at 2.0°C with a reversal of a wet tendency in the north and central Caribbean. The sub-regional variations that exist shows that although the Caribbean lags the globe in its attainment of the LTTGs some of its six subregions are more comparable to the global than the Caribbean mean with the transition from 1.5°C to 2.0°C seeming to represent a turning point for the Caribbean.</p>

Generating Projections for the Caribbean at 1.5, 2.0, and 2.5 °C from a High-Resolution Ensemble

Six members of the Hadley Centre’s Perturbed Physics Ensemble for the Quantifying Uncertainty in Model Predictions (QUMP) project are downscaled using the PRECIS (Providing Regional Climates for Impact Studies) RCM (Regional Climate Model). Climate scenarios at long-term temperature goals (LTTGs) of 1.5, 2.0, and 2.5 °C above pre-industrial warming levels are generated for the Caribbean and six sub-regions for annual and seasonal timescales. Under a high emissions scenario, the LTTGs are attained in the mid-2020s, end of the 2030s, and the early 2050s, respectively. At 1.5 °C, the region is slightly cooler than the globe, land areas warmer than ocean, and for the later months, the north is warmer than the south. The far western and southern Caribbean including the eastern Caribbean island chain dry at 1.5 °C (up to 50%). At 2.0 °C, the warming and drying intensify and there is a reversal of a wet tendency in parts of the north Caribbean. Drying in the rainfall season accounts for much of the annual change. There is limited further intensification of the region-wide drying at 2.5 °C. Changes in wind strength in the Caribbean low-level jet region may contribute to the patterns seen. There are implications for urgent and targeted adaptation planning in the Caribbean.

Can organic matter flux profiles be diagnosed using remineralisation rates derived from observed tracers and modelled ocean transport rates?

The average depth in the ocean at which the majority of sinking organic matter particles remineralise is a fundamental parameter in the oceans role in regulating atmospheric CO2. Observed spatial patterns in sinking fluxes and relationships between the fluxes of different particles in the modern ocean have widely been used to invoke controlling mechanisms with important implications for CO2 regulation. However, such analyses are limited by the sparse spatial sampling of the available sediment trap data. Here we explore whether model ocean circulation rates, in the form of a transport matrix, can be used to derive remineralisation rates and sinking particle flux curves from the much more highly resolved observations of dissolved nutrient concentrations. Initially we use the Earth system model GENIE to generate a synthetic tracer dataset to explore the methods and its sensitivity to key sources of uncertainty arising from errors in the tracer observations and in the model circulation. We use a perturbed physics ensemble to generate 54 different estimates of circulation to explore errors associated with model transport rates. We find that reconstructed remineralisation rates are highly sensitive to both errors in observations and our ensemble uncertainty in model circulation rates such that a simple inversion does not provide a robust estimate of particulate flux profiles. Inferred remineralisation rates are particularly sensitive to differences between the "observed" and modelled transport fluxes because remineralisation rates are 3–4 magnitudes smaller than circulation rates. We also find that when inferring particle flux curves from remineralisation rates the cycling of dissolved organic matter also creates biases that have a similar magnitude and spatial variability to flux curves diagnosed using sediment trap data. We end with a discussion on the potential future directions and pitfalls of estimating remineralisation rates using model circulation schemes.