Are you sure that your longitude data goes from -280 to 80 and not -180 to 80? Or perhaps from -180 to 180? There is no such thing as -280 degrees longitude.
Also, what is the grid spacing of your data? That is, what is the distance between your longitude and latitude values? Is it 2 degrees, 1 degree, 0.5 degree, 0.25 degree, etc. ?
Here is an example of how you can plot global temperature data using the imagescn function from the Climate Data Toolbox:
load global_sst.mat
figure(1)
h = imagescn(lon,lat,sst-273.15);
xlabel('Longitude')
ylabel('Latitude')
yticks(-90:30:90)
axis equal tight
colormap(turbo)
cb=colorbar;
cb.Label.String = 'Temperature (^\circC)';
